POWER ELECTRONICS PROJECTS - ABSTRACTS
A Bridgeless Boost Rectifier For Low-Voltage Energy Harvesting Applications
ABSTRACT
In this paper, a single-stage ac-dc power electronic converter is proposed to efficiently manage the energy harvested from electromagnetic microscale and mesoscale generators with low-voltage outputs.
The proposed topology combines a boost converter and a buck-boost converter to condition the positive and negative half portions of the input ac voltage, respectively. Only one inductor and capacitor are used in both circuitries to reduce the size of the converter.
A 2 cm × 2 cm, 3.34-g prototype has been designed and tested at 50-kHz switching frequency, which demonstrate 71% efficiency at 54.5 mW. The input ac voltage with 0.4-V amplitude is rectified and stepped up to 3.3-V dc. Detailed design guidelines are provided with the purpose of minimizing the size, weight, and power losses. The theoretical analyses are validated by the experiment results.
The proposed topology combines a boost converter and a buck-boost converter to condition the positive and negative half portions of the input ac voltage, respectively. Only one inductor and capacitor are used in both circuitries to reduce the size of the converter.
A 2 cm × 2 cm, 3.34-g prototype has been designed and tested at 50-kHz switching frequency, which demonstrate 71% efficiency at 54.5 mW. The input ac voltage with 0.4-V amplitude is rectified and stepped up to 3.3-V dc. Detailed design guidelines are provided with the purpose of minimizing the size, weight, and power losses. The theoretical analyses are validated by the experiment results.
A Controlled-Type Zvs Technique Without Auxiliary Components For The Low Power Dcac Inverter
ABSTRACT
This paper proposes a soft switching technique for dc/ac inverters, by using duty cycle and frequency modulation. Zero voltage switching (ZVS) is achieved through controlling the inductor current bidirectional in every switching cycle.
This technique requires no additional resonant components and can be employed for various low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes are derived from the basic theory of the proposed technique.
They are referred to as boundary current mode (BCM), variable hysteresis current mode (VHCM), and constant hysteresis current mode (CHCM) in this paper and their advantages and disadvantages are compared. Simulation and experimental results demonstrate the feasibilities of the proposed soft-switching technique and its control schemes.
This technique requires no additional resonant components and can be employed for various low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes are derived from the basic theory of the proposed technique.
They are referred to as boundary current mode (BCM), variable hysteresis current mode (VHCM), and constant hysteresis current mode (CHCM) in this paper and their advantages and disadvantages are compared. Simulation and experimental results demonstrate the feasibilities of the proposed soft-switching technique and its control schemes.
A Current Controller Design for Current Source Inverter-Fed AC Machine Drive System
ABSTRACT
A current source inverter (CSI) requires a capacitor filter for the commutation of switching device as well as for attenuating switching harmonics. Hence, the CSI-fed ac machine has a second-order system in the continuous time domain. This paper presents a design methodology for the closed-loop current controller of the CSI-fed ac machine drive system. A multiloop current controller design using a pole/zero cancellation method is employed with a transfer function matrix.
To decouple the cross-coupling terms which cause mutual interferences between the d- and q-axes in the synchronous reference frame, two types of controller are proposed and implemented using different decoupling method. Additionally, active damping methods are incorporated to enhance the stability of the system.
A stability analysis in discrete-time domain is investigated to verify the feasibility of the proposed closed-loop current controller. To evaluate the effectiveness of the proposed current controller, computer simulations and experimental tests were performed and the results are discussed.
To decouple the cross-coupling terms which cause mutual interferences between the d- and q-axes in the synchronous reference frame, two types of controller are proposed and implemented using different decoupling method. Additionally, active damping methods are incorporated to enhance the stability of the system.
A stability analysis in discrete-time domain is investigated to verify the feasibility of the proposed closed-loop current controller. To evaluate the effectiveness of the proposed current controller, computer simulations and experimental tests were performed and the results are discussed.
A DC–DC Converter based on the three-State Switching Cell for High Current and Voltage Step-Down Applications
ABSTRACT
This paper presents a pulsewidth modulation dc-dc nonisolated buck converter using the three-state switching cell, constituted by two active switches, two diodes, and two coupled inductors. Only part of the load power is processed by the active switches, reducing the peak current through the switches to half of the load current, as higher power levels can then be achieved by the proposed topology.
The volume of reactive elements, i.e., inductors and capacitors, is also decreased since the ripple frequency of the output voltage is twice the switching frequency. Due to the intrinsic characteristics of the topology, total losses are distributed among all semiconductors. Another advantage of this converter is the reduced region for discontinuous conduction mode when compared to the conventional buck converter or, in other words, the operation range in continuous conduction mode is increased, as demonstrated by the static gain plot.
The theoretical approach is detailed through qualitative and quantitative analyses by the application of the three-state switching cell to the buck converter operating in nonoverlapping mode (D <; 0.5). Besides, the mathematical analysis and development of an experimental prototype rated at 1 kW are carried out. The main experimental results are presented and adequately discussed to clearly identify its claimed advantages.
The volume of reactive elements, i.e., inductors and capacitors, is also decreased since the ripple frequency of the output voltage is twice the switching frequency. Due to the intrinsic characteristics of the topology, total losses are distributed among all semiconductors. Another advantage of this converter is the reduced region for discontinuous conduction mode when compared to the conventional buck converter or, in other words, the operation range in continuous conduction mode is increased, as demonstrated by the static gain plot.
The theoretical approach is detailed through qualitative and quantitative analyses by the application of the three-state switching cell to the buck converter operating in nonoverlapping mode (D <; 0.5). Besides, the mathematical analysis and development of an experimental prototype rated at 1 kW are carried out. The main experimental results are presented and adequately discussed to clearly identify its claimed advantages.
A Family of Three-Switch Three-State Single-Phase Z-Source Inverters
ABSTRACT
This paper proposes a new family of three-switch three-state single-phase Z-source inverters (TSTS-ZSIs) that can be classified into two groups, boost-based TSTS-ZSI and buck-boost-based TSTS-ZSI, according to the step-up circuit. All of the topologies have the merits of buck-boost capability and low voltage stress, and some of them have the feature of dual grounding.
In addition, the step-up in dc side and inversion in ac side is completely decoupled in the proposed topologies. In terms of a linear voltage gain, the conventional linear control methods can be used, which makes the control system very simple. The operating principles of the two types of topologies are described, respectively, and the comprehensive comparison between them is provided.
Finally, the theoretical analysis and comparison of the proposed topologies are verified by the simulation and experimental results.
In addition, the step-up in dc side and inversion in ac side is completely decoupled in the proposed topologies. In terms of a linear voltage gain, the conventional linear control methods can be used, which makes the control system very simple. The operating principles of the two types of topologies are described, respectively, and the comprehensive comparison between them is provided.
Finally, the theoretical analysis and comparison of the proposed topologies are verified by the simulation and experimental results.
A High Step-Down Transformer-Less Single-Stage Single-Switch ACDC Converter
ABSTRACT
This paper presents a high step-down tranformerless single-stage single-switch ac/dc converter suitable for universal line applications (90-270 Vrms) . The topology integrates a buck-type power-factor correction (PFC) cell with a buck-boost dc/dc cell and part of the input power is coupled to the output directly after the first power processing.
With this direct power transfer feature and sharing capacitor voltages, the converter is able to achieve efficient power conversion, high power factor, low voltage stress on intermediate bus (less than 130 V) and low output voltage without a high step-down transformer. The absence of transformer reduces the component counts and cost of the converter.
Unlike most of the boost-type PFC cell, the main switch of the proposed converter only handles the peak inductor current of dc/dc cell rather than the superposition of both inductor currents. Detailed analysis and design procedures of the proposed circuit are given and verified by experimental results.
With this direct power transfer feature and sharing capacitor voltages, the converter is able to achieve efficient power conversion, high power factor, low voltage stress on intermediate bus (less than 130 V) and low output voltage without a high step-down transformer. The absence of transformer reduces the component counts and cost of the converter.
Unlike most of the boost-type PFC cell, the main switch of the proposed converter only handles the peak inductor current of dc/dc cell rather than the superposition of both inductor currents. Detailed analysis and design procedures of the proposed circuit are given and verified by experimental results.
A High Step-Up Converter with a Voltage Multiplier Module for a Photovoltaic System
ABSTRACT
A novel high step-up converter is proposed for a front-end photovoltaic system. Through a voltage multiplier module, an asymmetrical interleaved high step-up converter obtains high step-up gain without operating at an extreme duty ratio. The voltage multiplier module is composed of a conventional boost converter and coupled inductors.
An extra conventional boost converter is integrated into the first phase to achieve a considerably higher voltage conversion ratio. The two-phase configuration not only reduces the current stress through each power switch, but also constrains the input current ripple, which decreases the conduction losses of metal-oxide-semiconductor field-effect transistors (MOSFETs). In addition, the proposed converter functions as an active clamp circuit, which alleviates large voltage spikes across the power switches.
Thus, the low-voltage-rated MOSFETs can be adopted for reductions of conduction losses and cost. Efficiency improves because the energy stored in leakage inductances is recycled to the output terminal. Finally, the prototype circuit with a 40-V input voltage, 380-V output, and 1000- W output power is operated to verify its performance. The highest efficiency is 96.8%.
An extra conventional boost converter is integrated into the first phase to achieve a considerably higher voltage conversion ratio. The two-phase configuration not only reduces the current stress through each power switch, but also constrains the input current ripple, which decreases the conduction losses of metal-oxide-semiconductor field-effect transistors (MOSFETs). In addition, the proposed converter functions as an active clamp circuit, which alleviates large voltage spikes across the power switches.
Thus, the low-voltage-rated MOSFETs can be adopted for reductions of conduction losses and cost. Efficiency improves because the energy stored in leakage inductances is recycled to the output terminal. Finally, the prototype circuit with a 40-V input voltage, 380-V output, and 1000- W output power is operated to verify its performance. The highest efficiency is 96.8%.
A High-Efficiency Positive Buck–Boost Converter with Mode-Select Circuit and Feed-Forward Techniques
ABSTRACT
This paper presents a high-efficiency positive buck- boost converter with mode-select circuits and feed-forward techniques. Four power transistors produce more conduction and more switching losses when the positive buck-boost converter operates in buck-boost mode.
Utilizing the mode-select circuit, the proposed converter can decrease the loss of switches and let the positive buck-boost converter operate in buck, buck-boost, or boost mode. By adding feed-forward techniques, the proposed converter can improve transient response when the supply voltages are changed.
The proposed converter has been fabricated with TSMC 0.35-μm CMOS 2P4M processes. The total chip area is 2.59 × 2.74 mm2 (with PADs), the output voltage is 3.3 V, and the regulated supply voltage range is from 2.5-5 V. Its switching frequency is 500 kHz and the maximum power efficiency is 91.6% as the load current equals 150 mA.
Utilizing the mode-select circuit, the proposed converter can decrease the loss of switches and let the positive buck-boost converter operate in buck, buck-boost, or boost mode. By adding feed-forward techniques, the proposed converter can improve transient response when the supply voltages are changed.
The proposed converter has been fabricated with TSMC 0.35-μm CMOS 2P4M processes. The total chip area is 2.59 × 2.74 mm2 (with PADs), the output voltage is 3.3 V, and the regulated supply voltage range is from 2.5-5 V. Its switching frequency is 500 kHz and the maximum power efficiency is 91.6% as the load current equals 150 mA.
A High-Performance SPWM Controller for Three-Phase UPS Systems Operating Under Highly Nonlinear Loads
ABSTRACT
This paper presents the design of a high-performance sinusoidal pulsewidth modulation (SPWM) controller for three-phase uninterruptible power supply (UPS) systems that are operating under highly nonlinear loads. The classical SPWM method is quite effective in controlling the RMS magnitude of the UPS output voltages. However, it is not good enough in compensating the harmonics and the distortion caused specifically by the nonlinear currents drawn by the rectifier loads.
The distortion becomes more severe at high power where the switching frequency has to be reduced due to the efficiency concerns. This study proposes a new design strategy that overcomes the limitations of the classical RMS control. It adds inner loops to the closed-loop control system effectively that enables successful reduction of harmonics and compensation of distortion at the outputs. Simulink is used to analyze, develop, and design the controller using the state-space model of the inverter.
The controller is implemented in the TMS320F2808 DSP by Texas Instruments, and the performance is evaluated experimentally using a three-phase 10 kVA transformer isolated UPS under all types of load conditions. In conclusion, the experimental results demonstrate that the controller successfully achieves the steady-state RMS voltage regulation specifications as well as the total harmonic distortion and the dynamic response requirements of major UPS standards.
The distortion becomes more severe at high power where the switching frequency has to be reduced due to the efficiency concerns. This study proposes a new design strategy that overcomes the limitations of the classical RMS control. It adds inner loops to the closed-loop control system effectively that enables successful reduction of harmonics and compensation of distortion at the outputs. Simulink is used to analyze, develop, and design the controller using the state-space model of the inverter.
The controller is implemented in the TMS320F2808 DSP by Texas Instruments, and the performance is evaluated experimentally using a three-phase 10 kVA transformer isolated UPS under all types of load conditions. In conclusion, the experimental results demonstrate that the controller successfully achieves the steady-state RMS voltage regulation specifications as well as the total harmonic distortion and the dynamic response requirements of major UPS standards.
A New Control Method of Interleaved Single-Stage Fly back AC–DC Converter for Outdoor Led Lighting Systems
ABSTRACT
In outdoor light-emitting diode (LED) lighting systems, there are a lot of applications. Depending on the output power rating, the power stage to drive an LED can be classified into single-stage and two-stage structures. The single-stage structure is for low-power LED lighting applications. However, it is difficult to apply at over 60-70 W of output power because of its low efficiency and huge transformer at high power.
On the other hand, the two-stage structure is usually used for high power applications. However, it is undesirable to cover wide output power range because of its poor power factor (PF) under the light load condition. To solve these problems, this paper proposes a new pulse duty cycle control method with pulse frequency modulation for an interleaved single-stage flyback ac-dc converter.
The proposed converter provides high efficiency under heavy loads with low ac line condition and under light loads with high ac line condition. In addition, the proposed converter shows high PF and low total harmonic distortion even when the output power is very low. As a result, a single LED ac-dc converter can cover wide power range for outdoor LED lighting applications. To verify the validity of the proposed converter, an 81-W prototype converter has been implemented and experimented on.
On the other hand, the two-stage structure is usually used for high power applications. However, it is undesirable to cover wide output power range because of its poor power factor (PF) under the light load condition. To solve these problems, this paper proposes a new pulse duty cycle control method with pulse frequency modulation for an interleaved single-stage flyback ac-dc converter.
The proposed converter provides high efficiency under heavy loads with low ac line condition and under light loads with high ac line condition. In addition, the proposed converter shows high PF and low total harmonic distortion even when the output power is very low. As a result, a single LED ac-dc converter can cover wide power range for outdoor LED lighting applications. To verify the validity of the proposed converter, an 81-W prototype converter has been implemented and experimented on.
A New DC Anti-Islanding Technique of Electrolytic Capacitor-Less Photovoltaic Interface in DC Distribution Systems
ABSTRACT
This paper proposes a photovoltaic (PV) generation system interfaced with a dc distribution system. DC interface allows for the improvement of system efficiency by fully utilizing dc-based renewable sources and storage devices. In this paper, issues on PV interface for dc distribution systems are discussed for energy-efficient and reliable system implementation. AC and dc PV interfaces are mathematically analyzed. In dc distribution, eliminating electrolytic capacitors in PV interfaces improves system reliability, increases system efficiency, and reduces cost. In addition, this paper proposes a new anti-islanding technique for dc distribution as a system protection scheme. The operating principle is presented in detail and analysis shows that the proposed injected current perturbation technique is an effective solution for anti-islanding operation.
A prototype converter features a simple structure with no electrolytic capacitor, which ensures a longer lifetime of the PV power circuit. Experimental results of the prototype circuit show a maximum efficiency of 98.1% and a European efficiency of 97.5%. The proposed anti-islanding technique shows fast response to the islanding condition in less than 0.2 s. It also shows that the average maximum power point tracking efficiency is 99.9% in normal conditions, which verifies the performance of the proposed scheme.
A Nonlinear Controller Based on a Discrete Energy Function for an ACDC Boost PFC Converter
ABSTRACT
AC/DC converter systems generally have two stages: an input power factor correction (PFC) boost ac/dc stage that converts input ac voltage to an intermediate dc voltage while reducing the input current harmonics injected to the grid, followed by a dc/dc converter that steps up or down the intermediate dc-bus voltage as required by the output load and provides high-frequency galvanic isolation.
Since a low-frequency ripple (second harmonic of the input ac line frequency) exists in the output voltage of the PFC ac/dc boost converter due to the power ripple, the voltage loop in the conventional control system must have a very low bandwidth in order to avoid distortions in the input current waveform. This results in the conventional PFC controller having a slow dynamic response against load variations with adverse overshoots and undershoots.
This paper presents a new control approach that is based on a novel discrete energy function minimization control law that allows the front-end ac/dc boost PFC converter to operate with faster dynamic response than the conventional controllers and simultaneously maintain near unity input power factor. Experimental results from a 3-kW ac/dc converter built for charging traction battery of a pure electric vehicle are presented in this paper to validate the proposed control method and its superiority over conventional controllers.
Since a low-frequency ripple (second harmonic of the input ac line frequency) exists in the output voltage of the PFC ac/dc boost converter due to the power ripple, the voltage loop in the conventional control system must have a very low bandwidth in order to avoid distortions in the input current waveform. This results in the conventional PFC controller having a slow dynamic response against load variations with adverse overshoots and undershoots.
This paper presents a new control approach that is based on a novel discrete energy function minimization control law that allows the front-end ac/dc boost PFC converter to operate with faster dynamic response than the conventional controllers and simultaneously maintain near unity input power factor. Experimental results from a 3-kW ac/dc converter built for charging traction battery of a pure electric vehicle are presented in this paper to validate the proposed control method and its superiority over conventional controllers.
A Single-Phase Grid-Connected Fuel Cell System based on a Boost-Inverter
ABSTRACT
In this paper, the boost-inverter topology is used as a building block for a single-phase grid-connected fuel cell (FC) system offering low cost and compactness. In addition, the proposed system incorporates battery-based energy storage and a dc-dc bidirectional converter to support the slow dynamics of the FC.
The single-phase boost inverter is voltage-mode controlled and the dc-dc bidirectional converter is current-mode controlled. The low-frequency current ripple is supplied by the battery which minimizes the effects of such ripple being drawn directly from the FC itself. Moreover, this system can operate either in a grid-connected or stand-alone mode.
In the grid-connected mode, the boost inverter is able to control the active (P) and reactive (Q) powers using an algorithm based on a second-order generalized integrator which provides a fast signal conditioning for single-phase systems. Design guidelines, simulation, and experimental results taken from a laboratory prototype are presented to confirm the performance of the proposed system.
The single-phase boost inverter is voltage-mode controlled and the dc-dc bidirectional converter is current-mode controlled. The low-frequency current ripple is supplied by the battery which minimizes the effects of such ripple being drawn directly from the FC itself. Moreover, this system can operate either in a grid-connected or stand-alone mode.
In the grid-connected mode, the boost inverter is able to control the active (P) and reactive (Q) powers using an algorithm based on a second-order generalized integrator which provides a fast signal conditioning for single-phase systems. Design guidelines, simulation, and experimental results taken from a laboratory prototype are presented to confirm the performance of the proposed system.
A Three-Level Converter with Reduced Filter Size using Two Transformers and Flying Capacitors
ABSTRACT
This paper proposes a pulse-width modulation (PWM) three-level converter with reduced filter size using two transformers. The proposed converter has many advantages. All switches sustain only the half of the input voltage and since the secondary rectified voltage is a three level waveform, the output filter inductor can be reduced.
Also, because of the power sharing of transformer and reduced output inductor, high efficiency can be obtained. The operational principle, analysis, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a prototype with 600W, 500-600V input, and 60V output.
Also, because of the power sharing of transformer and reduced output inductor, high efficiency can be obtained. The operational principle, analysis, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a prototype with 600W, 500-600V input, and 60V output.
Adaptive Dead-Time Compensation for Grid-Connected PWM Inverters of Single-Stage PV Systems
ABSTRACT
This study presents a new software-based plug-in dead-time compensator for grid-connected pulsewidth modulated voltage-source inverters of single-stage photovoltaic (PV) systems using predictive current controllers (PCCs) to regulate phase currents. First, a nonlinear dead-time disturbance model is reviewed, which is then used for the generation of a feed-forward compensation signal that eliminates the current distortion associated with current clamping effects around zero-current crossing points.
A novel closed-loop adaptive adjustment scheme is proposed for fine tuning in real time the compensation model parameters, thereby ensuring accurate results even under the highly varying operating conditions typically found in PV systems due to insolation, temperature, and shadowing effects, among others.
The algorithm implementation is straightforward and computationally efficient, and can be easily attached to an existent PCC to enhance its dead-time rejection capability without modifying its internal structure. Experimental results with a 5-kW PV system prototype are presented.
A novel closed-loop adaptive adjustment scheme is proposed for fine tuning in real time the compensation model parameters, thereby ensuring accurate results even under the highly varying operating conditions typically found in PV systems due to insolation, temperature, and shadowing effects, among others.
The algorithm implementation is straightforward and computationally efficient, and can be easily attached to an existent PCC to enhance its dead-time rejection capability without modifying its internal structure. Experimental results with a 5-kW PV system prototype are presented.
Adaptive Step Size with Adaptive-Perturbation - Frequency Digital MPPT Controller for a Single-Sensor Photovoltaic Solar System
ABSTRACT
This paper presents a load-current-based maximum power point tracking (MPPT) digital controller with an adaptive-step-size and adaptive-perturbation-frequency algorithm. Only one sensor is needed in the controller circuitry since the MPPT controller is only utilizing the load current information.
By utilizing a variable step-size algorithm, the speed, accuracy, and efficiency of the PV system MPPT are improved when compared to the fixed step-size load-current-based algorithm. Furthermore, the proposed adaptive algorithm utilizes a novel variable perturbation frequency scheme which further improves the controller speed.
The concept and operation of the load-current adaptive-step-size and adaptive-perturbation-frequency MPPT controller are presented, analyzed, and verified by results obtained from a proof-of-concept experimental prototype.
By utilizing a variable step-size algorithm, the speed, accuracy, and efficiency of the PV system MPPT are improved when compared to the fixed step-size load-current-based algorithm. Furthermore, the proposed adaptive algorithm utilizes a novel variable perturbation frequency scheme which further improves the controller speed.
The concept and operation of the load-current adaptive-step-size and adaptive-perturbation-frequency MPPT controller are presented, analyzed, and verified by results obtained from a proof-of-concept experimental prototype.
Adaptive Theory based Improved Linear Sinusoidal Tracer Control Algorithm for DSTATCOM
ABSTRACT
This paper presents a hardware implementation of three-phase distribution static compensator (DSTATCOM) using an adaptive theory-based improved linear sinusoidal tracer (ILST) control algorithm for different functions of DSTATCOM such as reactive power compensation for power factor correction, harmonics elimination, load balancing, and zero-voltage regulation under linear/nonlinear loads.
An ILST-based control algorithm is used for the extraction of fundamental load currents and their active and reactive power components. These components are used for the estimation of reference source currents.
A prototype of DSTATCOM is developed and its real-time performance is studied using a digital signal processor. The performance of DSTATCOM is found satisfactory with the proposed control algorithm under various types of loads.
An ILST-based control algorithm is used for the extraction of fundamental load currents and their active and reactive power components. These components are used for the estimation of reference source currents.
A prototype of DSTATCOM is developed and its real-time performance is studied using a digital signal processor. The performance of DSTATCOM is found satisfactory with the proposed control algorithm under various types of loads.
Adaptive Voltage Control of the DC-DC boost Stage in PV Converters with Small Input Capacitor
ABSTRACT
In the case of photovoltaic (PV) systems, an adequate PV voltage regulation is fundamental in order to both maximize and limit the power. For this purpose, a large input capacitor has traditionally been used. However, when reducing that capacitor's size, the nonlinearities of the PV array make the performance of the voltage regulation become highly dependent on the operating point.
This paper analyzes the nonlinear characteristics of the PV generator and clearly states their effect on the control of the dc/dc boost stage of commercial converters by means of a linearization around the operating point. Then, it proposes an adaptive control, which enables the use of a small input capacitor preserving at the same time the performance of the original system with a large capacitor.
Experimental results are carried out for a commercial converter with a 40 μF input capacitor, and a 4 kW PV array. The results corroborate the theoretical analysis; they evidence the problems of the traditional control, and validate the proposed control with such a small capacitor.
This paper analyzes the nonlinear characteristics of the PV generator and clearly states their effect on the control of the dc/dc boost stage of commercial converters by means of a linearization around the operating point. Then, it proposes an adaptive control, which enables the use of a small input capacitor preserving at the same time the performance of the original system with a large capacitor.
Experimental results are carried out for a commercial converter with a 40 μF input capacitor, and a 4 kW PV array. The results corroborate the theoretical analysis; they evidence the problems of the traditional control, and validate the proposed control with such a small capacitor.
Advanced Symmetrical Voltage Quad-Rupler Rectifiers for High Step-Up and High Output-Voltage Converters
ABSTRACT
An advanced symmetrical voltage quadrupler rectifier (SVQR) is derived in this paper to serve as the secondary rectification topology, which helps to extend the converter voltage gain and reduce the output diode voltage stresses.
The output voltage is four times of the conventional full-bridge voltage rectifier with the same transformer ratio, which benefits to reduce the turns ratio of the transformer and decrease the parasitic parameters. Also, low voltage-rated diodes with high switching performance can be applied to improve the efficiency. Meanwhile, all the diodes in SVQR have the same voltage and current stresses, which simplifies the thermal design.
Furthermore, two output electrolytic capacitors are connected in series to share the high output voltage, and the voltage balance can be realized naturally without any additional voltage-sharing scheme. A clear picture is made in this paper to give a general framework and universal applications for the derived SVQRs for high step-up and high output voltage conversion systems. A dual boost converter is used as an example to demonstrate the clear advantages of the derived SVQRs.
The output voltage is four times of the conventional full-bridge voltage rectifier with the same transformer ratio, which benefits to reduce the turns ratio of the transformer and decrease the parasitic parameters. Also, low voltage-rated diodes with high switching performance can be applied to improve the efficiency. Meanwhile, all the diodes in SVQR have the same voltage and current stresses, which simplifies the thermal design.
Furthermore, two output electrolytic capacitors are connected in series to share the high output voltage, and the voltage balance can be realized naturally without any additional voltage-sharing scheme. A clear picture is made in this paper to give a general framework and universal applications for the derived SVQRs for high step-up and high output voltage conversion systems. A dual boost converter is used as an example to demonstrate the clear advantages of the derived SVQRs.
An Adaptive Output Current Estimation Circuit for a Primary-Side Controlled Led Driver
ABSTRACT
A primary-side controlled method is commonly used in flyback LED driver to regulate output current by employing an auxiliary winding. However, owing to intrinsic propagation delay in real-world circuits, a primary-side controlled flyback converter experiences a worse line regulation.
This paper proposes a smart output current estimation scheme to improve line regulation for constant on-time control, and it can be compatible with the current flyback topology. A 9.5-W prototype of the proposed flyback LED driver has been fabricated in Nuvoton Technology Corporation 0.6-μm 5-V/40-V CMOS process.
The maximum switching frequency is set to around 100 kHz with universal-line input, single-stage power factor correction for LED lighting applications. Experimental results prove that the proposed scheme can improve the line regulation within 1.5% and the power efficiency can be up to 89.7%.
This paper proposes a smart output current estimation scheme to improve line regulation for constant on-time control, and it can be compatible with the current flyback topology. A 9.5-W prototype of the proposed flyback LED driver has been fabricated in Nuvoton Technology Corporation 0.6-μm 5-V/40-V CMOS process.
The maximum switching frequency is set to around 100 kHz with universal-line input, single-stage power factor correction for LED lighting applications. Experimental results prove that the proposed scheme can improve the line regulation within 1.5% and the power efficiency can be up to 89.7%.
An Improved Buck PFC Converter with High Power Factor
ABSTRACT
An improved buck power factor correction (PFC) converter topology is proposed in this paper. By adding an auxiliary switch and two diodes, the dead zones in ac input current of traditional buck PFC converter can be eliminated. An improved constant ON-time control is proposed and utilized in this improved buck PFC converter to force it that operates in critical conduction mode (CRM).
With optimal control parameters, nearly unit power factor can be achieved and the input current harmonics can meet the IEC61000-3-2 class C standard within the universal input voltage range. Moreover, the efficiency of the proposed converter is not deteriorated compared to the conventional buck converter.
Detailed theoretical analysis and optimal design considerations for the proposed converter are presented and verified by a 100-W lab-made prototype.
With optimal control parameters, nearly unit power factor can be achieved and the input current harmonics can meet the IEC61000-3-2 class C standard within the universal input voltage range. Moreover, the efficiency of the proposed converter is not deteriorated compared to the conventional buck converter.
Detailed theoretical analysis and optimal design considerations for the proposed converter are presented and verified by a 100-W lab-made prototype.
An Improved Soft-Switching Buck Converter with Coupled Inductor
ABSTRACT
An improved buck power factor correction (PFC) converter topology is proposed in this paper. By adding an auxiliary switch and two diodes, the dead zones in ac input current of traditional buck PFC converter can be eliminated.
An improved constant ON-time control is proposed and utilized in this improved buck PFC converter to force it that operates in critical conduction mode (CRM). With optimal control parameters, nearly unit power factor can be achieved and the input current harmonics can meet the IEC61000-3-2 class C standard within the universal input voltage range.
Moreover, the efficiency of the proposed converter is not deteriorated compared to the conventional buck converter. Detailed theoretical analysis and optimal design considerations for the proposed converter are presented and verified by a 100-W lab-made prototype.
An improved constant ON-time control is proposed and utilized in this improved buck PFC converter to force it that operates in critical conduction mode (CRM). With optimal control parameters, nearly unit power factor can be achieved and the input current harmonics can meet the IEC61000-3-2 class C standard within the universal input voltage range.
Moreover, the efficiency of the proposed converter is not deteriorated compared to the conventional buck converter. Detailed theoretical analysis and optimal design considerations for the proposed converter are presented and verified by a 100-W lab-made prototype.
An Improved Three-Phase Variable-Band Hysteresis Current Regulator
ABSTRACT
This paper presents an improved variable-band hysteresis current controller for a two-level three-phase voltage source inverter (VSI). The controller takes the average voltages of the phase-leg switched outputs as an approximation to the load back-EMF voltages, and uses these results to vary the hysteresis bands so as to maintain constant phase-leg switching frequencies.
The switching frequency control process is then further refined by fine tuning the hysteresis band variations to synchronize the zero crossings of the phase-leg current errors with a fixed reference clock so as to achieve a nearest space vector switching sequence, which further ensures that the switched output spectrum has been optimized.
Finally, a technique is proposed to replace the third phase-leg current regulator with a fixed-frequency open-loop pulse-width modulator, where its commanded reference is generated from the average switched output voltages of the other two phase legs. This avoids the hazard of the three independent hysteresis current regulators adversely interacting with each other in a conventional system, resulting from an overconstrained control problem with only two degrees of freedom.
Additionally, this approach allows the linear modulation range to be increased by adding a common-mode third-harmonic component to the third phase-leg reference command signal.
The switching frequency control process is then further refined by fine tuning the hysteresis band variations to synchronize the zero crossings of the phase-leg current errors with a fixed reference clock so as to achieve a nearest space vector switching sequence, which further ensures that the switched output spectrum has been optimized.
Finally, a technique is proposed to replace the third phase-leg current regulator with a fixed-frequency open-loop pulse-width modulator, where its commanded reference is generated from the average switched output voltages of the other two phase legs. This avoids the hazard of the three independent hysteresis current regulators adversely interacting with each other in a conventional system, resulting from an overconstrained control problem with only two degrees of freedom.
Additionally, this approach allows the linear modulation range to be increased by adding a common-mode third-harmonic component to the third phase-leg reference command signal.
An LLC Resonant DC–DC Converter for Wide Output Voltage Range Battery Charging Applications
ABSTRACT
In this paper, a control strategy is presented for a high performance LLC multi-resonant dc-dc converter in a two stage smart charger for neighborhood electric vehicle applications. It addresses several aspects and limitations of LLC resonant dc-dc converters in battery charging applications, such as very wide output voltage range while keeping the efficiency maximized, implementation of the current mode control at the secondary side and optimization of burst mode operation for current regulation at very low output voltage.
The proposed control scheme minimize both low and high frequency current ripple on the battery while maintaining stability of the dc-dc converter, thus maximizing battery life without penalizing the volume of the charger. Experimental results are presented for a prototype unit converting 390 V from the input dc link to an output voltage range of 48 V to 72 V dc at 650 W. The prototype achieves a peak efficiency of 96 %.
The proposed control scheme minimize both low and high frequency current ripple on the battery while maintaining stability of the dc-dc converter, thus maximizing battery life without penalizing the volume of the charger. Experimental results are presented for a prototype unit converting 390 V from the input dc link to an output voltage range of 48 V to 72 V dc at 650 W. The prototype achieves a peak efficiency of 96 %.
An Optimal Control Method for Photovoltaic Grid-Tied-Interleaved Fly back Micro inverters to Achieve High Efficiency in Wide Load Range
ABSTRACT
In this paper, a control strategy is presented for a high performance LLC multi-resonant dc-dc converter in a two stage smart charger for neighborhood electric vehicle applications. It addresses several aspects and limitations of LLC resonant dc-dc converters in battery charging applications, such as very wide output voltage range while keeping the efficiency maximized, implementation of the current mode control at the secondary side and optimization of burst mode operation for current regulation at very low output voltage.
The proposed control scheme minimize both low and high frequency current ripple on the battery while maintaining stability of the dc-dc converter, thus maximizing battery life without penalizing the volume of the charger. Experimental results are presented for a prototype unit converting 390 V from the input dc link to an output voltage range of 48 V to 72 V dc at 650 W. The prototype achieves a peak efficiency of 96 %.
The proposed control scheme minimize both low and high frequency current ripple on the battery while maintaining stability of the dc-dc converter, thus maximizing battery life without penalizing the volume of the charger. Experimental results are presented for a prototype unit converting 390 V from the input dc link to an output voltage range of 48 V to 72 V dc at 650 W. The prototype achieves a peak efficiency of 96 %.
Analysis and Design of a Push–Pull Quasi-Resonant Boost Power Factor Corrector
ABSTRACT
This paper proposes a novel power factor corrector (PFC) which is mainly composed of two-phase transition-mode (TM) boost-type power factor correctors (PFCs) and a coupled inductor. By integrating two boost inductors into one magnetic core, not only the circuit volume is reduced, but also the ripple current at the input side is lower. Therefore, both the power factor (PF) value and the power density are increased.
The proposed topology is capable of sharing the input current and output current equally. A cut-in-half duty cycle can reduce the conduction losses of the switches and both the turns and diameters of the inductor windings. The advantages of a TM boost PFC, such as quasi-resonant (QR) valley-switching on the switch and zero-current-switching (ZCS) of the output diode, are maintained to improve the overall conversion efficiency.
Detailed analysis and design procedures of the proposed topology are given. Simulations and experiments are conducted on a prototype with a universal line voltage, a 380-V output DC voltage and a 200-W output power to verify its feasibility.
The proposed topology is capable of sharing the input current and output current equally. A cut-in-half duty cycle can reduce the conduction losses of the switches and both the turns and diameters of the inductor windings. The advantages of a TM boost PFC, such as quasi-resonant (QR) valley-switching on the switch and zero-current-switching (ZCS) of the output diode, are maintained to improve the overall conversion efficiency.
Detailed analysis and design procedures of the proposed topology are given. Simulations and experiments are conducted on a prototype with a universal line voltage, a 380-V output DC voltage and a 200-W output power to verify its feasibility.
Analysis of a Fifth-Order Resonant Converter for High-Voltage DC Power Supplies
ABSTRACT
Power transformer is one of the most complex parts of power converters. The complicated behavior of the transformer is usually neglected in the power converter analysis and a simple model is mostly used to analyze the converter. This paper presents a precise analysis of a fifth-order resonant converter which has incorporated the resonant circuit into the transformer. The derived model, which is based on the accurate model of the power transformer, can fully predict the behavior of the fifth-order resonant converter.
The proposed fifth-order resonant converter is able to effectively reduce the range of phase-shift angle from no load to full load for a fixed-frequency phase-shift control approach. Therefore, the converter is able to operate under zero voltage switching during entire load range with a fixed-frequency control method. Also, the proposed converter offers a high gain which leads to a lower transformer turns ratio.
A 10-kVDC, 1.1-kW prototype has been prepared to evaluate the performance of the proposed converter. The experimental results exhibit the excellent accuracy of the proposed model and the superiority of the performance compared to the lower order resonant converters, especially for high-voltage applications.
The proposed fifth-order resonant converter is able to effectively reduce the range of phase-shift angle from no load to full load for a fixed-frequency phase-shift control approach. Therefore, the converter is able to operate under zero voltage switching during entire load range with a fixed-frequency control method. Also, the proposed converter offers a high gain which leads to a lower transformer turns ratio.
A 10-kVDC, 1.1-kW prototype has been prepared to evaluate the performance of the proposed converter. The experimental results exhibit the excellent accuracy of the proposed model and the superiority of the performance compared to the lower order resonant converters, especially for high-voltage applications.
Analysis, Design and Performance Evaluations of an Edge-Resonant Switched Capacitor Cell-Assisted Soft-Switching PWM Boost DC–DC Converter and its Interleaved Topology
ABSTRACT
This paper presents a soft-switching pulsewidth modulation (PWM) nonisolated boost dc-dc converter embedding an edge-resonant switched capacitor (ER-SWC) cell and its interleaved circuit topology. The conceptual boost dc-dc converter treated herein can achieve high-frequency zero-current soft-switching turn-on and zero-voltage soft-switching turn-off operations in the active switches and minimization of a reverse recovering current in the freewheeling diode under discontinuous conduction mode partially including critical conduction mode in the input current.
Those advantageous properties enable a wide range of soft-switching operations together with a high-voltage step-up conversion ratio with a reduced current stress. Circuit design guideline based on the soft-switching range is introduced; then, a theoretical analysis is carried out for investigating the step-up voltage conversion ratio.
For demonstrating the effectiveness of the ER-SWC soft-switching PWM boost dc-dc converter and its newly developed interleaved topology, laboratory prototypes are evaluated in experiments; then, their performances are discussed from a practical point of view.
Those advantageous properties enable a wide range of soft-switching operations together with a high-voltage step-up conversion ratio with a reduced current stress. Circuit design guideline based on the soft-switching range is introduced; then, a theoretical analysis is carried out for investigating the step-up voltage conversion ratio.
For demonstrating the effectiveness of the ER-SWC soft-switching PWM boost dc-dc converter and its newly developed interleaved topology, laboratory prototypes are evaluated in experiments; then, their performances are discussed from a practical point of view.
Analysis, Design and Experimental Results of a Novel Soft-Switching Snubberless Current-Fed Half-Bridge Front-End Converter-based PV Inverter
ABSTRACT
This paper proposes a new novel snubberless current-fed half-bridge front-end isolated dc/dc converter-based inverter for photovoltaic applications. It is suitable for grid-tied (utility interface) as well as off-grid (standalone) application based on the mode of control.
The proposed converter attains clamping of the device voltage by secondary modulation, thus eliminating the need of snubber or active-clamp. Zero-current switching or natural commutation of primary devices and zero-voltage switching of secondary devices is achieved. Soft-switching is inherent owing to the proposed secondary modulation and is maintained during wide variation in voltage and power transfer capacity and thus is suitable for photovoltaic (PV) applications.
Primary device voltage is clamped at reflected output voltage, and secondary device voltage is clamped at output voltage. Steady-state operation and analysis, and design procedure are presented. Simulation results using PSIM 9.0 are given to verify the proposed analysis and design.
An experimental converter prototype rated at 200 W has been designed, built, and tested in the laboratory to verify and demonstrate the converter performance over wide variations in input voltage and output power for PV applications. The proposed converter is a true isolated boost converter and has higher voltage conversion (boost) ratio compared to the conventional active-clamped converter.
The proposed converter attains clamping of the device voltage by secondary modulation, thus eliminating the need of snubber or active-clamp. Zero-current switching or natural commutation of primary devices and zero-voltage switching of secondary devices is achieved. Soft-switching is inherent owing to the proposed secondary modulation and is maintained during wide variation in voltage and power transfer capacity and thus is suitable for photovoltaic (PV) applications.
Primary device voltage is clamped at reflected output voltage, and secondary device voltage is clamped at output voltage. Steady-state operation and analysis, and design procedure are presented. Simulation results using PSIM 9.0 are given to verify the proposed analysis and design.
An experimental converter prototype rated at 200 W has been designed, built, and tested in the laboratory to verify and demonstrate the converter performance over wide variations in input voltage and output power for PV applications. The proposed converter is a true isolated boost converter and has higher voltage conversion (boost) ratio compared to the conventional active-clamped converter.
Analytical Modeling of Sideband Current Harmonic Components in Induction Machine Drive with Voltage Source Inverter by an SVM Technique
ABSTRACT
The sideband current harmonic components are practically inevitable in induction motor drive systems with voltage source inverter and pulse width modulation technique. However, those particular harmonic components would increase the losses, torque ripple, and electromagnetic noise so as to deteriorate the overall performance of the electric machine.
In this paper, the main sideband current harmonic components in induction machines driven by voltage source inverter with space vector pulse width modulation technique are analytically derived and expressed in both stator and synchronous dq reference frames, which could be employed as a rapid analytical tool to study the corresponding harmonic losses, torque pulsations, and electromagnetic noises.
The validity of the analytical models has been confirmed by the experimental results. Finally, both the load characteristics and impact factors on the sideband current harmonics in induction machine drives are comprehensively investigated and discussed based on the analytical models.
In this paper, the main sideband current harmonic components in induction machines driven by voltage source inverter with space vector pulse width modulation technique are analytically derived and expressed in both stator and synchronous dq reference frames, which could be employed as a rapid analytical tool to study the corresponding harmonic losses, torque pulsations, and electromagnetic noises.
The validity of the analytical models has been confirmed by the experimental results. Finally, both the load characteristics and impact factors on the sideband current harmonics in induction machine drives are comprehensively investigated and discussed based on the analytical models.
Application and Stability Analysis of a Novel Digital Active EMI Filter used in a Grid-Tied PV Microinverter Module
ABSTRACT
This paper presents a novel technique to suppress common-mode electromagnetic interference (EMI) using a digital active EMI filter (DAEF). The DAEF control technique is concurrently implemented with a digital controller of a grid-tied photovoltaic microinverter. A brief description of the microinverter architecture and its inverter circuit is illustrated.
The inverter stability is investigated using the overall transfer function. Accordingly, the system compensation is designed based on the direct quadrant (DQ) reference frame control technique. Finally, the proposed digital controller is tested on a grid-connected 200-W dc-ac microinverter. The experiment results validate the effectiveness of the proposed technique.
Compared with the conventional passive EMI filter, the proposed digital controller can achieve an equivalent or better performance in terms of EMI suppression and maintain stability within the operation bandwidth.
Therefore, the embedded DAEF can significantly reduce the size, cost, and space of the overall power inverter printed circuit board without the need of a conventional passive EMI filter.
The inverter stability is investigated using the overall transfer function. Accordingly, the system compensation is designed based on the direct quadrant (DQ) reference frame control technique. Finally, the proposed digital controller is tested on a grid-connected 200-W dc-ac microinverter. The experiment results validate the effectiveness of the proposed technique.
Compared with the conventional passive EMI filter, the proposed digital controller can achieve an equivalent or better performance in terms of EMI suppression and maintain stability within the operation bandwidth.
Therefore, the embedded DAEF can significantly reduce the size, cost, and space of the overall power inverter printed circuit board without the need of a conventional passive EMI filter.
Asymmetric Control of DC-Link Voltages for Separate MPPTSIN Three-Level Inverters
ABSTRACT
It is important to improve the overall efficiency of a photovoltaic (PV) inverter when it is connected to the grid. Fundamentally, the conversion efficiency from dc to ac power of an inverter is important. However, in the presence of partial shading, maximum power point tracking (MPPT) on PV modules is more important than the conversion efficiency.
In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible.
The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions.
In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible.
The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions.
Battery super capacitors Combination in Uninterruptible Power Supply (UPS)
ABSTRACT
The use of fuel cell technology as a backup power source for the uninterruptible power supply (UPS) requires quick response to sudden load change. However, slow dynamic behavior of a PEM fuel cell, compared to the typical power conditioner and load, limits the fuel cell rapid transient response to load change.
To increase the fuel cell response to load change, the energy storage such as battery, micro turbine, photovoltaic and super-capacitors are conventionally installed in the system thus increasing in its size and cost. In this work, the PEM fuel cell transient behaviors in the cool-start, hot-start and load change were investigated by using in-house running control software and high precise oscilloscope.
The effects of fuel cell structure (area of flow field, cell number and materials used in MEA) and operation conditions (pressure, temperature etc.) were also studied. The electrical response results from experimental curves indicate that the transient behavior of fuel cell stack is highly impacted by the fuel cell structure, operating conditions and the strategy of gas input into the fuel cell.
The better understanding of the electrical response of PEM fuel cell would be helpful to the design of a fuel cell and its system with high efficiency and compact structure.
To increase the fuel cell response to load change, the energy storage such as battery, micro turbine, photovoltaic and super-capacitors are conventionally installed in the system thus increasing in its size and cost. In this work, the PEM fuel cell transient behaviors in the cool-start, hot-start and load change were investigated by using in-house running control software and high precise oscilloscope.
The effects of fuel cell structure (area of flow field, cell number and materials used in MEA) and operation conditions (pressure, temperature etc.) were also studied. The electrical response results from experimental curves indicate that the transient behavior of fuel cell stack is highly impacted by the fuel cell structure, operating conditions and the strategy of gas input into the fuel cell.
The better understanding of the electrical response of PEM fuel cell would be helpful to the design of a fuel cell and its system with high efficiency and compact structure.
Bridgeless SEPIC Converter with a Ripple-Free Input Current
ABSTRACT
Conventional power factor correction (PFC) single-ended primary inductor converter (SEPIC) suffers from high conduction loss at the input bridge diode. To solve this problem, a bridgeless SEPIC converter with ripple-free input current is proposed.
In the proposed converter, the input bridge diode is removed and the conduction loss is reduced. In addition, the input current ripple is significantly reduced by utilizing an additional winding of the input inductor and an auxiliary capacitor. Similar to the conventional PFC SEPIC converter, the input current in a switching period is proportional to the input voltage and near unity power is achieved.
The operational principles, steady-state analysis, and design equations of the proposed converter are described in detail. Experimental results from a 130 W prototype at a constant switching frequency of 100 kHz are presented to verify the performance of the proposed converter.
In the proposed converter, the input bridge diode is removed and the conduction loss is reduced. In addition, the input current ripple is significantly reduced by utilizing an additional winding of the input inductor and an auxiliary capacitor. Similar to the conventional PFC SEPIC converter, the input current in a switching period is proportional to the input voltage and near unity power is achieved.
The operational principles, steady-state analysis, and design equations of the proposed converter are described in detail. Experimental results from a 130 W prototype at a constant switching frequency of 100 kHz are presented to verify the performance of the proposed converter.
Cascaded Multicell Trans-Z-Source Inverters
ABSTRACT
Inverters with high-output voltage gain usually face the problem of high-input current flowing through their components. The problem might further be exaggerated if the inverters use high-frequency magnetic devices like transformers or coupled inductors.
Leakage inductances of these devices must strictly be small to prevent overvoltages caused by switching of their winding currents. To avoid these related problems, cascaded trans-Z-source inverters are proposed. They use multiple magnetic cells in an alternately cascading pattern rather than a single magnetic cell with large turns ratio.
Simulation and experimental results have shown that the multicell inverters can produce the same high-voltage gain, while keeping currents and voltages of the components low. The inverters can also step down their output voltages like a traditional voltage-source inverter without compromising waveform quality.
Leakage inductances of these devices must strictly be small to prevent overvoltages caused by switching of their winding currents. To avoid these related problems, cascaded trans-Z-source inverters are proposed. They use multiple magnetic cells in an alternately cascading pattern rather than a single magnetic cell with large turns ratio.
Simulation and experimental results have shown that the multicell inverters can produce the same high-voltage gain, while keeping currents and voltages of the components low. The inverters can also step down their output voltages like a traditional voltage-source inverter without compromising waveform quality.
Class-DDE Dual-Mode-Operation Resonant Converter for Improved-Efficiency Domestic Induction Heating System
ABSTRACT
Induction heating (IH) technology is nowadays widely present in domestic appliances because of its cleanness, high efficiency, and faster heating process. All of these advantages are due to its heating process, where the pot is directly heated by the induced currents generated with a varying magnetic field.
As a result, the glass where the pot is supported is not directly heated and, consequently, efficiency and heating times are improved. IH systems are based on dc-link inverters to generate the required alternating current to feed the inductor. Usually, resonant converters are used to achieve higher efficiencies and power densities.
In such systems, the maximum output power and efficiency are achieved at the resonant frequency, and the switching frequency is increased to reduce the output power. As a consequence, in these converters, the efficiency is also reduced in the low-medium output power range.
This paper proposes the use of the half-bridge inverter in two operating modes to achieve higher efficiency in a wide output power range. The power converter topology can be reconfigured by changing the resonant capacitors through electromechanical relays. As a consequence, the entire efficiency of the cooking process is improved with a cost-effective procedure.
As a result, the glass where the pot is supported is not directly heated and, consequently, efficiency and heating times are improved. IH systems are based on dc-link inverters to generate the required alternating current to feed the inductor. Usually, resonant converters are used to achieve higher efficiencies and power densities.
In such systems, the maximum output power and efficiency are achieved at the resonant frequency, and the switching frequency is increased to reduce the output power. As a consequence, in these converters, the efficiency is also reduced in the low-medium output power range.
This paper proposes the use of the half-bridge inverter in two operating modes to achieve higher efficiency in a wide output power range. The power converter topology can be reconfigured by changing the resonant capacitors through electromechanical relays. As a consequence, the entire efficiency of the cooking process is improved with a cost-effective procedure.
Common-Mode Voltage Reduction Methods for Current-Source Converters in Medium-Voltage Drives
ABSTRACT
Common-mode voltages (CMVs) can lead to premature failure of the motor insulation system in medium-voltage current-source-fed drives. By analyzing the CMV values at all switching states under different operating conditions of a current-source-inverter (CSI)-based motor drive, this paper first indicates that the CMV peaks are produced by the zero states in most of the cases.
The nonzero-state (NZS) modulation techniques employed in voltage-source converters are adapted for use in a space-vector-modulated current-source converter (CSC) to reduce the CMV magnitude. For NZS modulation in CSCs, the nearest three-state (NTS) modulation sequences are designed with good low-order harmonic performances in their linear modulation region of ma ≥ 0.67 and with no increase in the device switching frequency.
A combined active-zero-state (AZS) modulation technique is also proposed as compensation, for a lower modulation index in the range of 0.4-0.67, when a compromise is made between the dc-link current minimization and high input power factor control. The simulation and experimental results are provided to validate the CMV reduction effects and harmonic performances of the NTS and combined AZS modulation methods in CSI-fed drives.
The nonzero-state (NZS) modulation techniques employed in voltage-source converters are adapted for use in a space-vector-modulated current-source converter (CSC) to reduce the CMV magnitude. For NZS modulation in CSCs, the nearest three-state (NTS) modulation sequences are designed with good low-order harmonic performances in their linear modulation region of ma ≥ 0.67 and with no increase in the device switching frequency.
A combined active-zero-state (AZS) modulation technique is also proposed as compensation, for a lower modulation index in the range of 0.4-0.67, when a compromise is made between the dc-link current minimization and high input power factor control. The simulation and experimental results are provided to validate the CMV reduction effects and harmonic performances of the NTS and combined AZS modulation methods in CSI-fed drives.
Control of Improved Full-Bridge Three-Level DC-DC Converter for Wind Turbines in a DC Grid
ABSTRACT
This paper presents an improved full-bridge three-level (IFBTL) dc/dc converter for a wind turbine in a dc grid by inserting a passive filter into the dc/dc converter to improve the performance of the converter. The passive filter can effectively reduce the voltage stress of the medium frequency transformer in the IFBTL dc/dc converter.
A modulation strategy, including two operation modes, is proposed for the IFBTL dc/dc converter. Then, a voltage balancing control strategy is proposed for the IFBTL dc/dc converter.
Furthermore, the control of the wind turbine based on the IFBTL dc/dc converter in a dc-grid system is presented. Finally, a small-scale IFBTL dc/dc converter prototype was built and tested in the laboratory, and the results verify the theoretical analysis.
A modulation strategy, including two operation modes, is proposed for the IFBTL dc/dc converter. Then, a voltage balancing control strategy is proposed for the IFBTL dc/dc converter.
Furthermore, the control of the wind turbine based on the IFBTL dc/dc converter in a dc-grid system is presented. Finally, a small-scale IFBTL dc/dc converter prototype was built and tested in the laboratory, and the results verify the theoretical analysis.
Control Strategy for Input-Series-Output-Series High-Frequency AC-Link Inverters
ABSTRACT
This paper presents a control strategy for input-series-output-series (ISOS) modular inverters. Each module is a bidirectional high-frequency ac-link (HFACL) inverter composed of an HF inverter, an HF transformer followed by a cycloconverter. The relationship between input voltage sharing (IVS) and output voltage sharing (OVS) is revealed with a general load based on bidirectional ISOS inverter systems.
To achieve IVS and OVS, a stable power sharing control strategy eliminating mandatory IVS loops is proposed. For individual modules, the common output voltage regulation loop output multiplies its magnitude compensator loop output to work as its pulse width modulation signal.
The loop gain design is also presented. With the proposed control strategy, excellent IVS and OVS can be obtained not only during steady state but also during transients. The effectiveness of the proposed control strategy is verified by simulation and experimental results of a 2420-VA ISOS two HFACL inverters.
To achieve IVS and OVS, a stable power sharing control strategy eliminating mandatory IVS loops is proposed. For individual modules, the common output voltage regulation loop output multiplies its magnitude compensator loop output to work as its pulse width modulation signal.
The loop gain design is also presented. With the proposed control strategy, excellent IVS and OVS can be obtained not only during steady state but also during transients. The effectiveness of the proposed control strategy is verified by simulation and experimental results of a 2420-VA ISOS two HFACL inverters.
DCM Analysis and Inductance Design Method of Interleaved Boost Converters
ABSTRACT
In order to use interleaved boost converters in the discontinuous conduction mode (DCM), the variation in the phase current and the input current ripple is analyzed theoretically. Based on the detailed analysis, a numerical formula for the input current ripple is deduced by including three criteria. Using the numerical formula, the optimized inductance that reduces the input current ripple and losses is deduced.
The boundary conduction mode (BCM) is also compared with the discontinuous conduction mode to verify their strong points. In order to verify the analysis, simulation and experimental results are compared with theoretical data.
The consideration of the BCM is also progressed by comparing with the DCM, and the results were different in terms of the efficiency and the input current ripple.
The boundary conduction mode (BCM) is also compared with the discontinuous conduction mode to verify their strong points. In order to verify the analysis, simulation and experimental results are compared with theoretical data.
The consideration of the BCM is also progressed by comparing with the DCM, and the results were different in terms of the efficiency and the input current ripple.
DC-Voltage Fluctuation Elimination through a DC-Capacitor Current Control for DFIG Converters under Unbalanced Grid Voltage Conditions
ABSTRACT
Unbalanced grid voltage causes a large second-order harmonic current in the dc-link capacitors as well as dc-voltage fluctuation, which potentially will degrade the lifespan and reliability of the capacitors in voltage source converters.
This paper proposes a novel dc-capacitor current control method for a grid-side converter (GSC) to eliminate the negative impact of unbalanced grid voltage on the dc-capacitors. In this method, a dc-capacitor current control loop, where a negative-sequence resonant controller is used to increase the loop gain, is added to the conventional GSC current control loop.
The rejection capability to the unbalanced grid voltage and the stability of the proposed control system are discussed. The second-order harmonic current in the dc capacitor as well as dc-voltage fluctuation is very well eliminated.
Hence, the dc capacitors will be more reliable under unbalanced grid voltage conditions. A modular implementation method of the proposed control strategy is developed for the DFIG controller. Finally, experiments are presented to validate the theoretical analysis.
This paper proposes a novel dc-capacitor current control method for a grid-side converter (GSC) to eliminate the negative impact of unbalanced grid voltage on the dc-capacitors. In this method, a dc-capacitor current control loop, where a negative-sequence resonant controller is used to increase the loop gain, is added to the conventional GSC current control loop.
The rejection capability to the unbalanced grid voltage and the stability of the proposed control system are discussed. The second-order harmonic current in the dc capacitor as well as dc-voltage fluctuation is very well eliminated.
Hence, the dc capacitors will be more reliable under unbalanced grid voltage conditions. A modular implementation method of the proposed control strategy is developed for the DFIG controller. Finally, experiments are presented to validate the theoretical analysis.
Design and Implementation of Energy Management System with Fuzzy Control for DC Microgrid Systems
ABSTRACT
This paper presents the design and implementation of an energy management system (EMS) with fuzzy control for a dc microgrid system. Modeling, analysis, and control of distributed power sources and energy storage devices with MATLAB/Simulink are proposed, and the integrated monitoring EMS is implemented with LabVIEW.
To improve the life cycle of the battery, fuzzy control manages the desired state of charge. The RS-485/ZigBee network has been designed to control the operating mode and to monitor the values of all subsystems in the dc microgrid system.
To improve the life cycle of the battery, fuzzy control manages the desired state of charge. The RS-485/ZigBee network has been designed to control the operating mode and to monitor the values of all subsystems in the dc microgrid system.
Design Methodology for a Very High Frequency Resonant Boost Converter
ABSTRACT
This paper introduces a design methodology for a resonant boost converter topology that is suitable for operation at very high frequencies. The topology we examine features a low parts count and fast transient response, but suffers from higher device stresses compared to other topologies that use a larger number of passive components. A numerical design procedure is developed for this topology that does not rely on time-domain simulation sweeps across parameters.
This allows the optimal converter design to be found for a particular main semiconductor switch. If an integrated power process is used where the designer has control over layout of the semiconductor switch, the optimal combination of converter design and semiconductor layout can be found.
To validate the proposed converter topology and design approach, a 75-MHz prototype converter is designed and experimentally demonstrated. The performance of the prototype closely matches that predicted by the design procedure, and the converter achieves good efficiency over a wide input voltage range.
This allows the optimal converter design to be found for a particular main semiconductor switch. If an integrated power process is used where the designer has control over layout of the semiconductor switch, the optimal combination of converter design and semiconductor layout can be found.
To validate the proposed converter topology and design approach, a 75-MHz prototype converter is designed and experimentally demonstrated. The performance of the prototype closely matches that predicted by the design procedure, and the converter achieves good efficiency over a wide input voltage range.
Design of High-Performance stand-Alone and Grid-Connected Inverter for Distributed Generation Applications
ABSTRACT
In this study, a high-performance inverter, including the functions of stand-alone and grid-connected power supplies, is developed so that distributed generation units can operate individually or in a microgrid mode. In the stand-alone power-supply mode, the output ac voltage can supply to ac loads.
In the grid-connected power-supply mode, the goal of power management can be achieved by controlling the amplitude and direction of the output current in the inverter. An adaptive total sliding-mode control (ATSMC) scheme is designed for the proposed high-performance inverter with a full-bridge framework.
As a result, the proposed high-performance inverter with the ATSMC scheme has the output voltage with a low total harmonic distortion in the stand-alone power-supply mode and the output current with a high power factor in the grid-connected power-supply mode to provide an ac output with high-performance power quality.
The effectiveness of the proposed high-performance inverter with the ATSMC is verified by experimental results of a 5-kW prototype, and the merit of the proposed ATSMC scheme is indicated in comparison with conventional proportional-integral and proportional-resonant control strategies.
In the grid-connected power-supply mode, the goal of power management can be achieved by controlling the amplitude and direction of the output current in the inverter. An adaptive total sliding-mode control (ATSMC) scheme is designed for the proposed high-performance inverter with a full-bridge framework.
As a result, the proposed high-performance inverter with the ATSMC scheme has the output voltage with a low total harmonic distortion in the stand-alone power-supply mode and the output current with a high power factor in the grid-connected power-supply mode to provide an ac output with high-performance power quality.
The effectiveness of the proposed high-performance inverter with the ATSMC is verified by experimental results of a 5-kW prototype, and the merit of the proposed ATSMC scheme is indicated in comparison with conventional proportional-integral and proportional-resonant control strategies.
Design Optimization of Transformerless Grid-Connected PV Inverters Including Reliability
ABSTRACT
This paper presents a new methodology for optimal design of transformerless photovoltaic (PV) inverters targeting a cost-effective deployment of grid-connected PV systems. The optimal switching frequency as well as the optimal values and types of the PV inverter components is calculated such that the PV inverter LCOE generated during the PV system lifetime period is minimized.
The LCOE is also calculated considering the failure rates of the components, which affect the reliability performance and lifetime maintenance cost of the PV inverter.
A design example is presented, demonstrating that compared to the nonoptimized PV inverter structures, the PV inverters designed using the proposed optimization methodology exhibit lower total manufacturing and lifetime maintenance cost and inject more energy into the electric-grid and by that minimizing LCOE.
The LCOE is also calculated considering the failure rates of the components, which affect the reliability performance and lifetime maintenance cost of the PV inverter.
A design example is presented, demonstrating that compared to the nonoptimized PV inverter structures, the PV inverters designed using the proposed optimization methodology exhibit lower total manufacturing and lifetime maintenance cost and inject more energy into the electric-grid and by that minimizing LCOE.
Design, Analysis and Implementation of Solar Power Optimizer for DC Distribution System
ABSTRACT
This paper proposes a high step-up solar power optimizer (SPO) that efficiently harvests maximum energy from a photovoltaic (PV) panel then outputs energy to a dc-microgrid. Its structure integrates coupled inductor and switched capacitor technologies to realize high step-up voltage gain.
The leakage inductance energy of the coupled inductor can be recycled to reduce voltage stress and power losses. A low voltage rating and low-conduction resistance switch improves system efficiency by employing the incremental conductance method for the maximum power point tracking (MPPT) algorithm.
Because of its high tracking accuracy, the method is widely used in the energy harvesting of PV systems. laboratory prototypes of the proposed SPO that have an input voltage range of 20 to 40 V and a maximum PV output power of 400 V/300 W are applied. The highest PV power conversion efficiency is 96.7%. The maximum MPPT accuracy is 99.9%, and the full load average MPPT accuracy is 97.8%.
The leakage inductance energy of the coupled inductor can be recycled to reduce voltage stress and power losses. A low voltage rating and low-conduction resistance switch improves system efficiency by employing the incremental conductance method for the maximum power point tracking (MPPT) algorithm.
Because of its high tracking accuracy, the method is widely used in the energy harvesting of PV systems. laboratory prototypes of the proposed SPO that have an input voltage range of 20 to 40 V and a maximum PV output power of 400 V/300 W are applied. The highest PV power conversion efficiency is 96.7%. The maximum MPPT accuracy is 99.9%, and the full load average MPPT accuracy is 97.8%.
Development and Operational Control of Two-String Maximum Power Point Trackers in DC Distribution Systems
ABSTRACT
This paper develops the operational control of two maximum power point trackers (MPPTs) for two-string photovoltaic (PV) panels in dc distribution systems. This dc distribution system is connected to ac grid via a bidirectional inverter.
Two PV strings and two MPPTs are implemented in this system. The proposed MPPT topology consists of buck and boost converters to deal with wide output voltage range of PV panels. To accurately determine the input current of MPPTs, the PV-string configuration check is accomplished online.
The perturbation and observation method are applied for maximum power point tracking. Moreover, the current balancing of two MPPT modules in parallel is achieved. In this paper, the system configuration and the operational principle of the proposed MPPT are first introduced. Afterward, the perturbation and observation method and the mode transition are demonstrated.
Flowcharts of the online PV-string configuration check and current balancing are explained. The validity of configuration check and current balancing is verified via the experimental results. Maximum power tracking performance and power conversion efficiency are also obtained.
Two PV strings and two MPPTs are implemented in this system. The proposed MPPT topology consists of buck and boost converters to deal with wide output voltage range of PV panels. To accurately determine the input current of MPPTs, the PV-string configuration check is accomplished online.
The perturbation and observation method are applied for maximum power point tracking. Moreover, the current balancing of two MPPT modules in parallel is achieved. In this paper, the system configuration and the operational principle of the proposed MPPT are first introduced. Afterward, the perturbation and observation method and the mode transition are demonstrated.
Flowcharts of the online PV-string configuration check and current balancing are explained. The validity of configuration check and current balancing is verified via the experimental results. Maximum power tracking performance and power conversion efficiency are also obtained.
Digital Plug-in Repetitive Controller for Single-Phase Bridgeless PFC Converters
ABSTRACT
This paper investigates a plug-in repetitive control scheme for bridgeless power factor correction (PFC) converters to mitigate input current distortions under continuous conduction mode and discontinuous conduction mode operating conditions.
From the PFC converter model and the fact that a type-II compensator is used, a design methodology to maximize the bandwidth of the feedback controller is suggested. After that, the error transfer function including the feedback controller is derived, and the stability of the repetitive control scheme is evaluated using the error transfer function.
The implementation of the digital repetitive controller is also discussed. The simulation and experimental results show that the input current THD is significantly improved by using the proposed control scheme for a 1-kW single-phase bridgeless PFC converter prototype.
From the PFC converter model and the fact that a type-II compensator is used, a design methodology to maximize the bandwidth of the feedback controller is suggested. After that, the error transfer function including the feedback controller is derived, and the stability of the repetitive control scheme is evaluated using the error transfer function.
The implementation of the digital repetitive controller is also discussed. The simulation and experimental results show that the input current THD is significantly improved by using the proposed control scheme for a 1-kW single-phase bridgeless PFC converter prototype.
Dual Transformerless Single-Stage Current Source Inverter with Energy Management Control Strategy
ABSTRACT
Alternative energy sources have for some time attracted great interest in the area of static converter development. This fact is related in greater part to issues such as sustainability and detrimental effects on the natural environment, which all contribute to the viability of this type of energy source.
In this context, power electronics performs important tasks making viable the connection of all these kind of clean power sources to the conventional grid and also to the load. From this perspective, a new challenge must be faced which is the development of energy management systems capable of providing intelligent planning and control of appliances in low- and high-power applications.
That being so, this paper intends to contribute presenting a novel dual transformerless single-stage current source inverter fed by a proton exchange membrane fuel cell (PEMFC) and a photovoltaic (PV) array. High voltage gain and totally controlled output voltage can be achieved without using dedicated step-up dc-dc converters or transformers either.
The main feature of this inverter structure is the intelligent power management technique which focuses on the extraction of maximum power from the PV array keeping the PEMFC as an energy storage system. Theoretical analysis is presented and corroborated by experimental results of a 400 W laboratory prototype.
In this context, power electronics performs important tasks making viable the connection of all these kind of clean power sources to the conventional grid and also to the load. From this perspective, a new challenge must be faced which is the development of energy management systems capable of providing intelligent planning and control of appliances in low- and high-power applications.
That being so, this paper intends to contribute presenting a novel dual transformerless single-stage current source inverter fed by a proton exchange membrane fuel cell (PEMFC) and a photovoltaic (PV) array. High voltage gain and totally controlled output voltage can be achieved without using dedicated step-up dc-dc converters or transformers either.
The main feature of this inverter structure is the intelligent power management technique which focuses on the extraction of maximum power from the PV array keeping the PEMFC as an energy storage system. Theoretical analysis is presented and corroborated by experimental results of a 400 W laboratory prototype.
Electric Equivalent Model for Induction Electrodeless Fluorescent Lamps
ABSTRACT
This paper presents an electric equivalent model applied to induction electrodeless fluorescent lamps. The model is based on passive components and takes into account the real and reactive lamp power.
The presented model and its obtention methodology will be an important tool for ballast designers. One of the most important features of the proposed methodology is the concern regarding core losses and lamp reactive characteristics, because nowadays there are no electric models including these characteristics. In order to obtain and validate the electrodeless lamp model, a series-parallel resonant half-bridge inverter is used as ballast.
Plasma and lamp windings are modeled as resistances and reactances depending on the lamp power. Simulations employing the proposed model are also presented, showing an excellent agreement with experimental results.
The presented model and its obtention methodology will be an important tool for ballast designers. One of the most important features of the proposed methodology is the concern regarding core losses and lamp reactive characteristics, because nowadays there are no electric models including these characteristics. In order to obtain and validate the electrodeless lamp model, a series-parallel resonant half-bridge inverter is used as ballast.
Plasma and lamp windings are modeled as resistances and reactances depending on the lamp power. Simulations employing the proposed model are also presented, showing an excellent agreement with experimental results.
Enhanced Control of a DFIG-based Wind-Power Generation System with Series Grid-Side Converter Under Unbalanced Grid Voltage Conditions
ABSTRACT
This paper presents an enhanced control method for a doubly fed induction generator (DFIG)-based wind-power generation system with series grid-side converter (SGSC) under unbalanced grid voltage conditions. The behaviors of the DFIG system with SGSC during network unbalance are described.
By injecting a series control voltage generated from the SGSC to balance the stator voltage, the adverse effects of voltage unbalance upon the DFIG, such as stator and rotor current unbalances, electromagnetic torque, and power pulsations, can be removed, and then the conventional vector control strategy for the rotor-side converter remains in full force under unbalanced conditions.
Meanwhile, three control targets for the parallel grid-side converter (PGSC) are identified, including eliminating the oscillations in the total active power or reactive power, or eliminating negative-sequence current injected to the grid. Furthermore, a precise current reference generation strategy for the PGSC has been proposed for the PGSC to further improve the operation performance of the whole system.
Finally, the proposed coordinated control strategy for the DFIG system with SGSC has been validated by the simulation results of a 2-MW-DFIG-based wind turbine with SGSC and experimental results on a laboratory-scale experimental rig under small steady-state grid voltage unbalance.
By injecting a series control voltage generated from the SGSC to balance the stator voltage, the adverse effects of voltage unbalance upon the DFIG, such as stator and rotor current unbalances, electromagnetic torque, and power pulsations, can be removed, and then the conventional vector control strategy for the rotor-side converter remains in full force under unbalanced conditions.
Meanwhile, three control targets for the parallel grid-side converter (PGSC) are identified, including eliminating the oscillations in the total active power or reactive power, or eliminating negative-sequence current injected to the grid. Furthermore, a precise current reference generation strategy for the PGSC has been proposed for the PGSC to further improve the operation performance of the whole system.
Finally, the proposed coordinated control strategy for the DFIG system with SGSC has been validated by the simulation results of a 2-MW-DFIG-based wind turbine with SGSC and experimental results on a laboratory-scale experimental rig under small steady-state grid voltage unbalance.
Generalized Multicell Switched-Inductor and Switched-Capacitor Z-Source Inverters
ABSTRACT
Traditional voltage-source inverter is limited by its only voltage step-down operation, while current-source inverter is limited by its only current step-down mode. In order to add an extra boosting flexibility while keeping the number of active semiconductors unchanged, voltage-type and current-type Z-source inverters were earlier proposed.
These new classes of inverters are generally more robust and less sensitive to electromagnetic noises. However, their boosting capabilities are somehow compromised by high component stresses and poorer spectral performances caused by low modulation ratios.
Their boosting gains are, therefore, limited in practice. To overcome these shortcomings, the generalized switched-inductor and switched-capacitor Z-source inverters are proposed, whose extra boosting abilities and other advantages have already been verified in simulation and experiment.
These new classes of inverters are generally more robust and less sensitive to electromagnetic noises. However, their boosting capabilities are somehow compromised by high component stresses and poorer spectral performances caused by low modulation ratios.
Their boosting gains are, therefore, limited in practice. To overcome these shortcomings, the generalized switched-inductor and switched-capacitor Z-source inverters are proposed, whose extra boosting abilities and other advantages have already been verified in simulation and experiment.
Grid Interfacing of Multimegawatt Photovoltaic Inverters
ABSTRACT
This paper investigates the suitability of selective harmonic elimination (SHE) for low-loss multimegawatt grid-connected photovoltaic (PV) inverters. The proposed system is able to meet utilities regulations, IEEE and IEC standards.
In an attempt to substantiate the potential superiority of SHE over carrier-based or space-vector pulsewidth modulation (PWM), this paper demonstrates that SHE may allow grid-connected PV inverters to be controlled using a switching frequency of less than 1 kHz, while the inverter is still able to provide necessary operation features such as independent control of active and reactive powers and operation control simplicity.
For system validation, experimental results with SHE are compared to the case when the inverter is controlled using third-harmonic injection PWM, with a 2-kHz switching frequency. Furthermore, the paper proposes a new implementation technique for SHE that utilizes the third harmonics to spread the switching angles over 90° instead of being located in a narrow range as generated when using conventional techniques, along with increases in modulation index.
The advantages of the proposed technique include simplicity in implementation and flexibility in PWM waveforms. Simulation and experimentation demonstrate agreement, which validates the practicability of the proposed system.
In an attempt to substantiate the potential superiority of SHE over carrier-based or space-vector pulsewidth modulation (PWM), this paper demonstrates that SHE may allow grid-connected PV inverters to be controlled using a switching frequency of less than 1 kHz, while the inverter is still able to provide necessary operation features such as independent control of active and reactive powers and operation control simplicity.
For system validation, experimental results with SHE are compared to the case when the inverter is controlled using third-harmonic injection PWM, with a 2-kHz switching frequency. Furthermore, the paper proposes a new implementation technique for SHE that utilizes the third harmonics to spread the switching angles over 90° instead of being located in a narrow range as generated when using conventional techniques, along with increases in modulation index.
The advantages of the proposed technique include simplicity in implementation and flexibility in PWM waveforms. Simulation and experimentation demonstrate agreement, which validates the practicability of the proposed system.
High Boost Ratio Hybrid Transformer DC–DC Converter for Photovoltaic Module Applications
ABSTRACT
This paper presents a non-isolated, high boost ratio hybrid transformer dc-dc converter with applications for low voltage renewable energy sources. The proposed converter utilizes a hybrid transformer to transfer the inductive and capacitive energy simultaneously, achieving a high boost ratio with a smaller size magnetic component.
As a result of incorporating the resonant operation mode into the traditional high boost ratio PWM converter, the turn off loss of the switch is reduced, increasing the efficiency of the converter under all load conditions.
The input current ripple is also reduced because of the linear-sinusoidal hybrid waveforms. The voltage stresses on the active switch and diodes are maintained at a low level and are independent of the changing input voltage over a wide range as a result of the resonant capacitor transferring energy to the output.
The effectiveness of the proposed converter was experimentally verified using a 220 W prototype circuit. Utilizing an input voltage ranging from 20V to 45V and a load range of 30W to 220W, the experimental results show system of efficiencies greater than 96% with a peak efficiency of 97.4% at 35V input, 160W output.
Because of high efficiency over wide output power range and the ability to operate with a wide variable input voltage, the proposed converter is an attractive design for alternative low dc voltage energy sources, such as solar photovoltaic (PV) modules.
As a result of incorporating the resonant operation mode into the traditional high boost ratio PWM converter, the turn off loss of the switch is reduced, increasing the efficiency of the converter under all load conditions.
The input current ripple is also reduced because of the linear-sinusoidal hybrid waveforms. The voltage stresses on the active switch and diodes are maintained at a low level and are independent of the changing input voltage over a wide range as a result of the resonant capacitor transferring energy to the output.
The effectiveness of the proposed converter was experimentally verified using a 220 W prototype circuit. Utilizing an input voltage ranging from 20V to 45V and a load range of 30W to 220W, the experimental results show system of efficiencies greater than 96% with a peak efficiency of 97.4% at 35V input, 160W output.
Because of high efficiency over wide output power range and the ability to operate with a wide variable input voltage, the proposed converter is an attractive design for alternative low dc voltage energy sources, such as solar photovoltaic (PV) modules.
High Boost Ratio Hybrid Transformer DC–DC Converter for Photovoltaic Module Applications
ABSTRACT
This paper proposes new multi-channel LEDs driving methods in electrolytic capacitor-less, single-stage AC-DC drivers which use current transformer(CT) to sense output current in constant current control and operate without any damage when the number of LED channels increase or decrease.
To increase lifetime of the power supply, electrolytic capacitor is substituted to small polyester film capacitor. And to insure input power factor(PF) higher than 0.9, conventional Buck-Boost PFC converter is chosen due to its simplicity and low cost. The converter operates in boundary mode condition between CCM and DCM to achieve soft switching and high efficiency.
In order to verify the performance of new multi-channel LEDs driving method in constant current control, a 35V, 1.3A(45W) Buck-Boost PFC converter was designed and tested to drive 2-channel LED arrays with each 2.2uF polyester film capacitor. Through test and experiment, it was verified that the proposed methods operated very well regardless of the number of LED channels.
To increase lifetime of the power supply, electrolytic capacitor is substituted to small polyester film capacitor. And to insure input power factor(PF) higher than 0.9, conventional Buck-Boost PFC converter is chosen due to its simplicity and low cost. The converter operates in boundary mode condition between CCM and DCM to achieve soft switching and high efficiency.
In order to verify the performance of new multi-channel LEDs driving method in constant current control, a 35V, 1.3A(45W) Buck-Boost PFC converter was designed and tested to drive 2-channel LED arrays with each 2.2uF polyester film capacitor. Through test and experiment, it was verified that the proposed methods operated very well regardless of the number of LED channels.
High-Efficiency Asymmetrical Half-Bridge Converter without Electrolytic Capacitor for Low-Output-Voltage AC–DC Led Drivers
ABSTRACT
Due to their high reliability and luminous efficacy, high-brightness light-emitting diodes are being widely used in lighting applications, and therefore, their power supplies are required to have also high reliability and efficiency. A very common approach for achieving this in ac-dc applications is using a two-stage topology.
The power factor corrector boost converter operating in the boundary conduction mode is a very common converter used as first stage. It is normally designed without electrolytic capacitors, improving reliability but also increasing the low-frequency ripple of the output voltage.
The asymmetrical half-bridge (AHB) is a perfect option for the second stage as it has very high efficiency, it operates at constant switching frequency, and its output filter is small (i.e., it can be also easily implemented without electrolytic capacitors). Moreover, the AHB is an excellent candidate for self-driven synchronous rectification (SD-SR) as its transformer does not have dead times. However, the standard configuration of the SD-SR must be modified in this case in order to deal with the transformer voltage variations due to the input voltage ripple and, more important, due to the LED dimming state. This modification is presented in this paper.
Another important issue regarding the AHB is that its closed-loop controller cannot be very fast and it cannot easily cancel the previously mentioned low-frequency ripple. In this paper, a feed-forward technique, specifically designed to overcome this problem, is also presented.
The experimental results obtained with a 60-W topology show that efficiency of the AHB may be very high (94.5%), while the inherent control problems related to the AHB can be overcome by the proposed feed-forward technique.
The power factor corrector boost converter operating in the boundary conduction mode is a very common converter used as first stage. It is normally designed without electrolytic capacitors, improving reliability but also increasing the low-frequency ripple of the output voltage.
The asymmetrical half-bridge (AHB) is a perfect option for the second stage as it has very high efficiency, it operates at constant switching frequency, and its output filter is small (i.e., it can be also easily implemented without electrolytic capacitors). Moreover, the AHB is an excellent candidate for self-driven synchronous rectification (SD-SR) as its transformer does not have dead times. However, the standard configuration of the SD-SR must be modified in this case in order to deal with the transformer voltage variations due to the input voltage ripple and, more important, due to the LED dimming state. This modification is presented in this paper.
Another important issue regarding the AHB is that its closed-loop controller cannot be very fast and it cannot easily cancel the previously mentioned low-frequency ripple. In this paper, a feed-forward technique, specifically designed to overcome this problem, is also presented.
The experimental results obtained with a 60-W topology show that efficiency of the AHB may be very high (94.5%), while the inherent control problems related to the AHB can be overcome by the proposed feed-forward technique.
High-Efficiency Isolated Bi-directional AC–DC Converter for a DC Distribution System
ABSTRACT
A high-efficiency isolated bidirectional ac–dc converter is proposed for a 380-V dc power distribution system to control bidirectional power flows and to improve its power conversion efficiency. To reduce the switches’ losses of the proposed nonisolated full-bridge ac–dc rectifier using an unipolar switching method, switching devices employ insulated-gate bipolar transistors, MOSFETs, and silicon carbide diodes.
Using the analysis of the rectifier’s operating modes, each switching device can be selected by considering switch stresses. A simple and intuitive frequency detection method for a single-phase synchronous reference frame-phase-locked loop (SRF-PLL) is also proposed using a filter compensator, a fast period detector, and a finite impulse response filter to improve the robustness and accuracy of PLL performance under fundamental frequency variations.
In addition, design and control methodology of the bidirectional full-bridge CLLC resonant converter is suggested for the galvanic isolation of the dc distribution system. A dead-band control algorithm for the bidirectional dc–dc converter is developed to smoothly change power conversion directions only using output voltage information. Experimental results will verify the performance of the proposed methods using a 5-kW prototype converter.
Using the analysis of the rectifier’s operating modes, each switching device can be selected by considering switch stresses. A simple and intuitive frequency detection method for a single-phase synchronous reference frame-phase-locked loop (SRF-PLL) is also proposed using a filter compensator, a fast period detector, and a finite impulse response filter to improve the robustness and accuracy of PLL performance under fundamental frequency variations.
In addition, design and control methodology of the bidirectional full-bridge CLLC resonant converter is suggested for the galvanic isolation of the dc distribution system. A dead-band control algorithm for the bidirectional dc–dc converter is developed to smoothly change power conversion directions only using output voltage information. Experimental results will verify the performance of the proposed methods using a 5-kW prototype converter.
High-Efficiency Led Driver without Electrolytic Capacitor for Street Lighting
ABSTRACT
High-Brightness Light Emitting Diodes (HB-LEDs) are considered as a remarkable lighting device due to their high reliability, chromatic variety and increasing efficiency. As a consequence, a high number of solutions for supplying LED strings are coming out. One-stage solutions are cost-effective, but their efficiency is low as they have to fulfill several purposes with only one converter: Power Factor Correction (PFC), galvanic isolation (in some cases) and current regulation.
Two-stage and three-stage solutions have higher efficiency as each stage is optimized for just one or two tasks and they are the preferred option when supplying several strings at the same time. Nevertheless, due to their higher cost in comparison to one-stage solutions, they are used when high-efficiency, high-performance and the possibility of supplying several strings are the main concerns. Besides, they are also used when high reliability is needed and electrolytic capacitors cannot be used.
In this paper, a three-stage solution and its complete design guideline for LED-based applications is proposed. PFC is achieved by a Boost converter while the galvanic isolation is provided by an Electronic Transformer (second stage). The third stages (one for each LED string) are designed following the TIBuck schematic, but taking advantage of the load characteristics (i.e., the high value of the LED string knee voltage, approximately equal to half the string nominal voltage).
Besides, a variation of the analog driving technique is also proposed. Experimental results obtained with a 160-W prototype show an efficiency as high as 93% for the whole topology and 95% for the cascade connection of the second and third stages.
Two-stage and three-stage solutions have higher efficiency as each stage is optimized for just one or two tasks and they are the preferred option when supplying several strings at the same time. Nevertheless, due to their higher cost in comparison to one-stage solutions, they are used when high-efficiency, high-performance and the possibility of supplying several strings are the main concerns. Besides, they are also used when high reliability is needed and electrolytic capacitors cannot be used.
In this paper, a three-stage solution and its complete design guideline for LED-based applications is proposed. PFC is achieved by a Boost converter while the galvanic isolation is provided by an Electronic Transformer (second stage). The third stages (one for each LED string) are designed following the TIBuck schematic, but taking advantage of the load characteristics (i.e., the high value of the LED string knee voltage, approximately equal to half the string nominal voltage).
Besides, a variation of the analog driving technique is also proposed. Experimental results obtained with a 160-W prototype show an efficiency as high as 93% for the whole topology and 95% for the cascade connection of the second and third stages.
High-Efficiency Single-Input Multiple-Output DC–DC Converter
ABSTRACT
The aim of this study is to develop a high-efficiency single-input multiple-output (SIMO) dc-dc converter. The proposed converter can boost the voltage of a low-voltage input power source to a controllable high-voltage dc bus and middle-voltage output terminals.
The high-voltage dc bus can take as the main power for a high-voltage dc load or the front terminal of a dc-ac inverter. Moreover, middle-voltage output terminals can supply powers for individual middle-voltage dc loads or for charging auxiliary power sources (e.g., battery modules).
In this study, a coupled-inductor-based dc-dc converter scheme utilizes only one power switch with the properties of voltage clamping and soft switching, and the corresponding device specifications are adequately designed. As a result, the objectives of high-efficiency power conversion, high step-up ratio, and various output voltages with different levels can be obtained.
Some experimental results via a kilowatt-level prototype are given to verify the effectiveness of the proposed SIMO dc-dc converter in practical applications.
The high-voltage dc bus can take as the main power for a high-voltage dc load or the front terminal of a dc-ac inverter. Moreover, middle-voltage output terminals can supply powers for individual middle-voltage dc loads or for charging auxiliary power sources (e.g., battery modules).
In this study, a coupled-inductor-based dc-dc converter scheme utilizes only one power switch with the properties of voltage clamping and soft switching, and the corresponding device specifications are adequately designed. As a result, the objectives of high-efficiency power conversion, high step-up ratio, and various output voltages with different levels can be obtained.
Some experimental results via a kilowatt-level prototype are given to verify the effectiveness of the proposed SIMO dc-dc converter in practical applications.
Hybrid-Frequency Modulation for PWM-Integrated Resonant Converters
ABSTRACT
This paper presents a unique modulation method for extending the input range of pulse-width modulation (PWM)-integrated resonant converters, such as the isolated boost resonant converter, while maintaining high conversion efficiency. The technique includes primarily the hybridizing of constant-on, constant-off, and fixed-frequency control depending only on the required duty cycle.
The modulation scheme reduces core loss and conduction loss dramatically by decreasing the applied volt-seconds at the transformer and improving the switching period utilization. With hybrid-frequency control, the circuit also maintains zero current switching for the output diodes, minimizes switching loss, and eliminates circulating energy at the transformer across the entire operating range.
It also allows for a predictable voltage gain, dependent only on duty cycle and transformer turns ratio. A detailed loss analysis is provided and verified against a 180 W experimental prototype, with an input range of 12-48 V and a switching frequency range of 30-70 kHz.
Implementation issues are also handled with a variety of solutions for realizing the modulation scheme. Experimental results show greater than 4% weighted efficiency improvement in the prototype using the proposed method.
The modulation scheme reduces core loss and conduction loss dramatically by decreasing the applied volt-seconds at the transformer and improving the switching period utilization. With hybrid-frequency control, the circuit also maintains zero current switching for the output diodes, minimizes switching loss, and eliminates circulating energy at the transformer across the entire operating range.
It also allows for a predictable voltage gain, dependent only on duty cycle and transformer turns ratio. A detailed loss analysis is provided and verified against a 180 W experimental prototype, with an input range of 12-48 V and a switching frequency range of 30-70 kHz.
Implementation issues are also handled with a variety of solutions for realizing the modulation scheme. Experimental results show greater than 4% weighted efficiency improvement in the prototype using the proposed method.
Improved Sensorless Operation of a CSI-Based Induction Motor Drive Long Feeder Case
ABSTRACT
Various applications, like in underground mines and oil and gas industries, require remote operation of vector-controlled medium-voltage variable speed drives via a long motor feeder. The use of voltage source inverters in such cases leads to motor overvoltage and harmonic quality problems.
The current source inverter (CSI) is ideally matched to these applications because of its motor-friendly voltage output. Speed sensorless operation is mandatory due to the long motor feeder. Although the model reference adaptive system (MRAS) is a powerful and proven speed estimation tool, its implementation in long motor feeder drives faces many challenges.
Among them, and addressed in this paper, are inherent dc offset in its stator model, the need for actual motor voltage and current values, and oscillations in the estimated speed due to errors in the motor current measurement signals.
In this paper, a sensorless CSI vector-controlled drive, suitable for long motor feeder applications, is studied. Improved speed estimation is achieved by proposing 1) a modified dc-offset eliminator for an MRAS speed estimation and 2) a compensation technique for motor current's measurement errors. Intensive experimental results, for a low-voltage scaled model, along with simulations validate the effectiveness of the proposed technique.
The current source inverter (CSI) is ideally matched to these applications because of its motor-friendly voltage output. Speed sensorless operation is mandatory due to the long motor feeder. Although the model reference adaptive system (MRAS) is a powerful and proven speed estimation tool, its implementation in long motor feeder drives faces many challenges.
Among them, and addressed in this paper, are inherent dc offset in its stator model, the need for actual motor voltage and current values, and oscillations in the estimated speed due to errors in the motor current measurement signals.
In this paper, a sensorless CSI vector-controlled drive, suitable for long motor feeder applications, is studied. Improved speed estimation is achieved by proposing 1) a modified dc-offset eliminator for an MRAS speed estimation and 2) a compensation technique for motor current's measurement errors. Intensive experimental results, for a low-voltage scaled model, along with simulations validate the effectiveness of the proposed technique.
Improved Voltage-Vector Sequences on Dead-Beat Predictive Direct Power Control of Reversible Three-Phase Grid-Connected Voltage-Source Converters
ABSTRACT
This paper presents a dead-beat predictive direct power control (DPC) strategy and its improved voltage-vector sequences for reversible three-phase grid-connected voltage-source converters (VSCs). The instantaneous variation rates of active and reactive powers, by applying each converter voltage vector in 12 different sectors, are deduced and analyzed.
Based on the power variation rates, it is found that the values of the predicted duration times for the two conventional active converter voltage vectors are less than zero when the grid-connected VSC operates as either a rectifier or an inverter.
In order to solve this issue, two new alternative vector sequences are proposed and compared. Experimental results on a 1.5 kW reversible grid-connected VSC system are presented to validate the feasibility of the proposed voltage-vector sequences on the dead-beat predictive DPC strategy.
Based on the power variation rates, it is found that the values of the predicted duration times for the two conventional active converter voltage vectors are less than zero when the grid-connected VSC operates as either a rectifier or an inverter.
In order to solve this issue, two new alternative vector sequences are proposed and compared. Experimental results on a 1.5 kW reversible grid-connected VSC system are presented to validate the feasibility of the proposed voltage-vector sequences on the dead-beat predictive DPC strategy.
Input Differential-Mode EMI of CRM Boost PFC Converter
ABSTRACT
In this paper, the differential-mode (DM) electromagnetic interference (EMI) noise of a single-phase boost power factor correction converter operating in critical current mode was analyzed.
The DM noise spectra are calculated based on the mathematical model of EMI receiver and the required corner frequencies of DM filter are obtained. It can be seen that the minimum corner frequencies are determined by the maximum noises at 150 kHz. With the relation between the magnitude of the inductor current ripple and the DM noise, the characteristics of noise at 150 kHz are obtained by analyzing the current ripple magnitude at 150 kHz; thus, the worst conditions which have the maximum noise value are figured out.
Meanwhile, the maximum noises at 150 kHz for different input voltages are identical, so the DM filter can be designed based on one worst spectrum at one input voltage without testing the spectra in other conditions.
The DM noise spectra are calculated based on the mathematical model of EMI receiver and the required corner frequencies of DM filter are obtained. It can be seen that the minimum corner frequencies are determined by the maximum noises at 150 kHz. With the relation between the magnitude of the inductor current ripple and the DM noise, the characteristics of noise at 150 kHz are obtained by analyzing the current ripple magnitude at 150 kHz; thus, the worst conditions which have the maximum noise value are figured out.
Meanwhile, the maximum noises at 150 kHz for different input voltages are identical, so the DM filter can be designed based on one worst spectrum at one input voltage without testing the spectra in other conditions.
Integration and Operation of a Single-Phase Bidirectional Inverter with Two Buck boost MPPTS for DC-Distribution Applications
ABSTRACT
This study is focused on integration and operation of a single-phase bidirectional inverter with two buck/boost maximum power point trackers (MPPTs) for dc-distribution applications. In a dc-distribution system, a bidirectional inverter is required to control the power flow between dc bus and ac grid, and to regulate the dc bus to a certain range of voltages.
A droop regulation mechanism according to the inverter inductor current levels to reduce capacitor size, balance power flow, and accommodate load variation is proposed. Since the photovoltaic (PV) array voltage can vary from 0 to 600 V, especially with thin-film PV panels, the MPPT topology is formed with buck and boost converters to operate at the dc-bus voltage around 380 V, reducing the voltage stress of its followed inverter.
Additionally, the controller can online check the input configuration of the two MPPTs, equally distribute the PV-array output current to the two MPPTs in parallel operation, and switch control laws to smooth out mode transition.
A comparison between the conventional boost MPPT and the proposed buck/boost MPPT integrated with a PV inverter is also presented. Experimental results obtained from a 5-kW system have verified the discussion and feasibility.
A droop regulation mechanism according to the inverter inductor current levels to reduce capacitor size, balance power flow, and accommodate load variation is proposed. Since the photovoltaic (PV) array voltage can vary from 0 to 600 V, especially with thin-film PV panels, the MPPT topology is formed with buck and boost converters to operate at the dc-bus voltage around 380 V, reducing the voltage stress of its followed inverter.
Additionally, the controller can online check the input configuration of the two MPPTs, equally distribute the PV-array output current to the two MPPTs in parallel operation, and switch control laws to smooth out mode transition.
A comparison between the conventional boost MPPT and the proposed buck/boost MPPT integrated with a PV inverter is also presented. Experimental results obtained from a 5-kW system have verified the discussion and feasibility.
Interleaved Boost Converter with Ripple Cancellation Network
ABSTRACT
This paper presents an interleaved boost converter (IBC) with ripple cancellation network (RCN). Based on the conventional IBC, two capacitors, two coupled inductors, and two inductors are added as RCN in the proposed converter.
Therefore, the proposed converter shares the same advantages of the conventional IBC and achieves input current ripple cancellation without significantly increasing the current stress and loss of the converter.
Finally, a 36-V input voltage, 50-V output voltage, and 1-kW output power prototype circuit operating at 100 kHz is implemented in the laboratory to verify the expected performance.
The proposed converter can achieve input current ripple cancellation in all power range with the efficiency higher than 96%. The simulation and experimental results show that the proposed IBC with RCN has great potential to be applied in high-power, high-efficiency dc/dc conversion.
Therefore, the proposed converter shares the same advantages of the conventional IBC and achieves input current ripple cancellation without significantly increasing the current stress and loss of the converter.
Finally, a 36-V input voltage, 50-V output voltage, and 1-kW output power prototype circuit operating at 100 kHz is implemented in the laboratory to verify the expected performance.
The proposed converter can achieve input current ripple cancellation in all power range with the efficiency higher than 96%. The simulation and experimental results show that the proposed IBC with RCN has great potential to be applied in high-power, high-efficiency dc/dc conversion.
Interleaved Boundary Conduction Mode (BCM) Buck Power Factor Correction (PFC) Converter
ABSTRACT
An interleaved boundary conduction mode power-factor-correction buck converter that maintains high efficiency across entire load and line range is proposed. The adaptive master-slave interleaving method maintains stable 180° out-of-phase operation during any transient.
By interleaving two parallel-connected buck converters, the input current ripple is halved while the ripple frequency is doubled, which leads to a smaller differential mode line filter. The line current harmonic distortion is analyzed to examine the allowable output voltage range while meeting harmonic regulations. The operation and performance of the proposed circuit is verified on a 300 W, universal line experimental prototype with 80 V output.
The measured efficiencies remain above 96% down to 20% of full load across the entire universal line range. Even at 10% of full-load condition, the efficiency remains above 94%. The input current harmonics also meet the IEC61000-3-2 (class D) standard.
By interleaving two parallel-connected buck converters, the input current ripple is halved while the ripple frequency is doubled, which leads to a smaller differential mode line filter. The line current harmonic distortion is analyzed to examine the allowable output voltage range while meeting harmonic regulations. The operation and performance of the proposed circuit is verified on a 300 W, universal line experimental prototype with 80 V output.
The measured efficiencies remain above 96% down to 20% of full load across the entire universal line range. Even at 10% of full-load condition, the efficiency remains above 94%. The input current harmonics also meet the IEC61000-3-2 (class D) standard.
Interleaved High Step-Up ZVT Converter with Built-in Transformer Voltage Doubler Cell for Distributed PV Generation System
ABSTRACT
In this paper, the concept of built-in transformer voltage doubler cell is derived to generate an improved interleaved high step-up converter for distributed photovoltaic generation applications. The proposed built-in transformer voltage doubler cell is composed of three transformer windings, two voltage doubler diodes, and two voltage doubler capacitors.
The voltage doubler capacitors are charged and discharged alternatively to double the voltage gain. The switch duty cycle and the transformer turns ratio can be employed as two controllable freedoms to lift the voltage ratio flexibly.
The power device voltage stress can also be reduced to improve the circuit performance. Furthermore, the active clamp scheme is adopted to recycle the leakage energy, absorb the switch turn-off voltage spikes, and achieve zero-voltage switching (ZVS) operation for all active switches.
Meanwhile, the diode reverse-recovery problem is alleviated by the leakage inductance of the built-in transformer. All these factors benefit the circuit performance improvements in the high step-up and large current applications. Finally, a 1-kW prototype with 40-380 V conversion is built and tested to demonstrate the effectiveness of the proposed converter.
The voltage doubler capacitors are charged and discharged alternatively to double the voltage gain. The switch duty cycle and the transformer turns ratio can be employed as two controllable freedoms to lift the voltage ratio flexibly.
The power device voltage stress can also be reduced to improve the circuit performance. Furthermore, the active clamp scheme is adopted to recycle the leakage energy, absorb the switch turn-off voltage spikes, and achieve zero-voltage switching (ZVS) operation for all active switches.
Meanwhile, the diode reverse-recovery problem is alleviated by the leakage inductance of the built-in transformer. All these factors benefit the circuit performance improvements in the high step-up and large current applications. Finally, a 1-kW prototype with 40-380 V conversion is built and tested to demonstrate the effectiveness of the proposed converter.
Light-Load Efficiency Improvement in Buck-Derived Single-Stage Single-Switch PFC Converters
ABSTRACT
Single-stage single-switch ac/dc converters with power factor correction (PFC) generally have higher power losses under a light-load condition, as compared to that of the two-stage approach, due to the sharing of a common power transistor such that the PFC stage cannot be switched OFF separately to save power losses.
This letter addresses this problem by using a buck topology for the PFC stage of the single-stage single-switch converters as it can be completely turned OFF by operating the converter only near the zero crossing of the input voltage, due to the presence of the dead angle of input current. Hence, the switching and conduction losses to the transistor and diodes, and passive devices are reduced.
Also, further improvement is made by finding the best combination of dc-bus capacitor charging time and discharging time to achieve the lowest power loss. A recently proposed converter topology which combines a buck PFC cell with a buck-boost dc/dc cell is used as an example.
Experimental results are reported and confirmed that the proposed light-load power loss reduction scheme on the converter can improve power stage efficiency by up to 7% at 1 W of output power as compared to that without the proposed scheme.
This letter addresses this problem by using a buck topology for the PFC stage of the single-stage single-switch converters as it can be completely turned OFF by operating the converter only near the zero crossing of the input voltage, due to the presence of the dead angle of input current. Hence, the switching and conduction losses to the transistor and diodes, and passive devices are reduced.
Also, further improvement is made by finding the best combination of dc-bus capacitor charging time and discharging time to achieve the lowest power loss. A recently proposed converter topology which combines a buck PFC cell with a buck-boost dc/dc cell is used as an example.
Experimental results are reported and confirmed that the proposed light-load power loss reduction scheme on the converter can improve power stage efficiency by up to 7% at 1 W of output power as compared to that without the proposed scheme.
Light-to-Light PV-Fed Led Lighting Systems
ABSTRACT
This paper discusses the principle of operation, dynamic modeling, and control design for light-to-light (LtL) systems, whose aim is to directly convert the sun irradiation into artificial light.
The system discussed in this paper is composed by a photovoltaic (PV) panel, an LED array, a dc-dc converter dedicated to the maximum power point tracking of the PV panel and a dc-dc converter dedicated to drive the LEDs array.
A system controller is also included, whose goal is to ensure the matching between the maximum available PV power and the LED power by means of a low-frequency LEDs dimming. An experimental design example is discussed to illustrate the functionalities of the LtL system.
The system discussed in this paper is composed by a photovoltaic (PV) panel, an LED array, a dc-dc converter dedicated to the maximum power point tracking of the PV panel and a dc-dc converter dedicated to drive the LEDs array.
A system controller is also included, whose goal is to ensure the matching between the maximum available PV power and the LED power by means of a low-frequency LEDs dimming. An experimental design example is discussed to illustrate the functionalities of the LtL system.
Mitigation of Lower Order Harmonics in a Grid-Connected Single-Phase PV Inverter
ABSTRACT
In this paper, a simple single-phase grid-connected photovoltaic (PV) inverter topology consisting of a boost section, a low-voltage single-phase inverter with an inductive filter, and a step-up transformer interfacing the grid is considered. Ideally, this topology will not inject any lower order harmonics into the grid due to high-frequency pulse width modulation operation.
However, the nonideal factors in the system such as core saturation-induced distorted magnetizing current of the transformer and the dead time of the inverter, etc., contribute to a significant amount of lower order harmonics in the grid current. A novel design of inverter current control that mitigates lower order harmonics is presented in this paper. An adaptive harmonic compensation technique and its design are proposed for the lower order harmonic compensation.
In addition, a proportional-resonant-integral (PRI) controller and its design are also proposed. This controller eliminates the dc component in the control system, which introduces even harmonics in the grid current in the topology considered.
The dynamics of the system due to the interaction between the PRI controller and the adaptive compensation scheme is also analyzed. The complete design has been validated with experimental results and good agreement with theoretical analysis of the overall system is observed.
However, the nonideal factors in the system such as core saturation-induced distorted magnetizing current of the transformer and the dead time of the inverter, etc., contribute to a significant amount of lower order harmonics in the grid current. A novel design of inverter current control that mitigates lower order harmonics is presented in this paper. An adaptive harmonic compensation technique and its design are proposed for the lower order harmonic compensation.
In addition, a proportional-resonant-integral (PRI) controller and its design are also proposed. This controller eliminates the dc component in the control system, which introduces even harmonics in the grid current in the topology considered.
The dynamics of the system due to the interaction between the PRI controller and the adaptive compensation scheme is also analyzed. The complete design has been validated with experimental results and good agreement with theoretical analysis of the overall system is observed.
Modeling and Simulation of All-Electric Ships with Low-Voltage DC Hybrid Power Systems
ABSTRACT
DC hybrid power systems are of interest for future low emission, fuel-efficient vessels. In spite of the advantages they offer onboard a ship, they result in a complex, interconnected system, which requires effective analysis tools to enable a full realization of the advantages. Modeling and simulation are essential tools to facilitate design, analysis, and optimization of the system.
This paper reviews modeling of hybrid electric ship components including mechanical and electrical elements. Power electronic converters are modeled by nonlinear averaging methods to suit system-level studies. A unified model for bidirectional converters is proposed to avoid transitions between two separate models.
A simulation platform using the derived models is developed for the system-level analysis of hybrid electric ships. Simulation results of power sharing among two diesel generators, a fuel cell module, and an energy storage system are presented for three modes of operation.
This paper reviews modeling of hybrid electric ship components including mechanical and electrical elements. Power electronic converters are modeled by nonlinear averaging methods to suit system-level studies. A unified model for bidirectional converters is proposed to avoid transitions between two separate models.
A simulation platform using the derived models is developed for the system-level analysis of hybrid electric ships. Simulation results of power sharing among two diesel generators, a fuel cell module, and an energy storage system are presented for three modes of operation.
Multilevel DC-Link Inverter and Control Algorithm to Overcome the PV Partial Shading
ABSTRACT
This letter presents for the first time the application of multilevel dc-link inverter to overcome the problem of partial shading of individual photovoltaic (PV) sources which are connected in series. The “PV permutation algorithm,” as a new method, is developed for the control of the inverter so as to extract the maximum power form each PV source under partial shading and to deliver all that power to the load.
The algorithm is based on combination of the direct pulsewidth modulation, the sequential permutation PV sources, and the output generation to control the multilevel dc-link inverter.
The algorithm is applied successfully to a seven-level inverter with separate maximum power point tracking algorithm for each PV source and under nonuniform irradiance (partial shading).
Digital processing unit F28335 eZdsp is used to control the PV system in the real-time mode, and MATLAB-Simulink real-time data exchange is employed to display the extracted power and to control the system parameters via a designed graphical user interface window. The implementation and experimental results are presented.
The algorithm is based on combination of the direct pulsewidth modulation, the sequential permutation PV sources, and the output generation to control the multilevel dc-link inverter.
The algorithm is applied successfully to a seven-level inverter with separate maximum power point tracking algorithm for each PV source and under nonuniform irradiance (partial shading).
Digital processing unit F28335 eZdsp is used to control the PV system in the real-time mode, and MATLAB-Simulink real-time data exchange is employed to display the extracted power and to control the system parameters via a designed graphical user interface window. The implementation and experimental results are presented.
Precise Accelerated Torque Control for Small Inductance brushless DC Motor
ABSTRACT
In this paper, precise accelerated torque control for a small inductance brushless dc motor (BLDCM) is achieved by electromagnetic torque control and disturbance torque suppression. First, the electromagnetic torque ripple is reduced in commutation and conduction regions.
In the former region, the ripple is suppressed by overlapping commutation control and optimizing the duty ratio of the active controller. In the latter region, the unbalance ripple caused by the unbalanced three phase windings is reduced by the proposed asymmetry compensation function, and the disturbance ripple created by the back electromotive force (EMF) is compensated by feedforward control.
Second, the disturbance torque has been observed and compensated through the improved disturbance torque controller whose compensation coefficient is obtained by line-to-line back EMF coefficient estimation.
And, both the disturbance observation and speed measurement are all synchronized with the encoder pulse alteration. Experimental results are presented to demonstrate the validity and effectiveness of the proposed accelerated torque control scheme.
In the former region, the ripple is suppressed by overlapping commutation control and optimizing the duty ratio of the active controller. In the latter region, the unbalance ripple caused by the unbalanced three phase windings is reduced by the proposed asymmetry compensation function, and the disturbance ripple created by the back electromotive force (EMF) is compensated by feedforward control.
Second, the disturbance torque has been observed and compensated through the improved disturbance torque controller whose compensation coefficient is obtained by line-to-line back EMF coefficient estimation.
And, both the disturbance observation and speed measurement are all synchronized with the encoder pulse alteration. Experimental results are presented to demonstrate the validity and effectiveness of the proposed accelerated torque control scheme.
Problems Incurred in a Vector-Controlled Single-Phase Induction Motor, and a Proposal for a Vector-Controlled Two-Phase Induction Motor as a Replacement
ABSTRACT
This paper presents several of the problems encountered with vector-controlled single-phase induction motor (SPIM), and discusses about the complex implementation of a vector controlled SPIM drive.
The vector-controlled symmetrical two-phase induction motor (TPIM) is presented as a viable replacement for the vector-controlled SPIM. The implementation of the proposed vector-controlled TPIM is simple compared to the vector-controlled SPIM. All the TPIM parameters can be calculated simply and precisely.
The proposed strategy for TPIM is derived from the indirect vector control strategy used for three-phase ac machines. Several differences between the vector control strategies for the TPIM and for three-phase ac motor are discussed. The validity of the proposed vector-controlled TPIM was verified by simulations and experiments.
The vector-controlled symmetrical two-phase induction motor (TPIM) is presented as a viable replacement for the vector-controlled SPIM. The implementation of the proposed vector-controlled TPIM is simple compared to the vector-controlled SPIM. All the TPIM parameters can be calculated simply and precisely.
The proposed strategy for TPIM is derived from the indirect vector control strategy used for three-phase ac machines. Several differences between the vector control strategies for the TPIM and for three-phase ac motor are discussed. The validity of the proposed vector-controlled TPIM was verified by simulations and experiments.
Reduced-Order Model and Control Approach for the Boost Converter with a Voltage Multiplier Cell
ABSTRACT
The boost converter with a voltage multiplier cell allows the static gain extension by means of the switching capacitor technique, reducing the duty cycle needed to achieve the same voltage gain when compared to the conventional boost converter. However, the modeling of this converter is complex and requires the use of advanced techniques due to the resonant inductor.
Thus, this paper aims to present a reduced-order model of this converter without the resonant energy exchange between the capacitors, so that the state-space averaging technique can be applied assuming small ripple in the state variables. In addition, this paper presents the design of a control system for the boost converter with a voltage multiplier cell.
The adopted strategy employs an inner loop to control the input current and an outer loop for the output voltage regulation. Extensive analysis based on simulations and an experimental prototype demonstrate that the proposed modeling, although simplified, is sufficient for an adequate control system design, ensuring good voltage regulation, and fast transient responses.
Thus, this paper aims to present a reduced-order model of this converter without the resonant energy exchange between the capacitors, so that the state-space averaging technique can be applied assuming small ripple in the state variables. In addition, this paper presents the design of a control system for the boost converter with a voltage multiplier cell.
The adopted strategy employs an inner loop to control the input current and an outer loop for the output voltage regulation. Extensive analysis based on simulations and an experimental prototype demonstrate that the proposed modeling, although simplified, is sufficient for an adequate control system design, ensuring good voltage regulation, and fast transient responses.
Series Asymmetrical Half-Bridge Converters with Voltage Auto balance for High Input-Voltage Applications
ABSTRACT
In this paper, an isolated series asymmetrical half-bridge converter (SA-HBC) is proposed. The SA-HBC circuit consists of two series half-bridge cells, sharing one leakage inductance and one transformer.
Two advantages make SA-HBC suitable for the high input voltage applications: (a) the voltage stress of each switch is reduced to half of the input voltage; (b) the voltages across the input capacitors are automatically balanced by the inherent switched capacitor technique, without additional circuits or control methods. Moreover, zero-voltage-switching (ZVS) condition is achieved for all switches.
The operational principles, circuit performance including output voltage, ZVS condition and voltage-auto-balance scheme of SA-HBC are analyzed in detail. And all these analyses are confirmed by the experimental results from a prototype with 500–600V input and 48V/20A output.
Two advantages make SA-HBC suitable for the high input voltage applications: (a) the voltage stress of each switch is reduced to half of the input voltage; (b) the voltages across the input capacitors are automatically balanced by the inherent switched capacitor technique, without additional circuits or control methods. Moreover, zero-voltage-switching (ZVS) condition is achieved for all switches.
The operational principles, circuit performance including output voltage, ZVS condition and voltage-auto-balance scheme of SA-HBC are analyzed in detail. And all these analyses are confirmed by the experimental results from a prototype with 500–600V input and 48V/20A output.
Soft-Switching DC-DC Converter with a Full ZVS Range and Reduced Output Filter for High-Voltage Applications
ABSTRACT
Power conversion from an input voltage of several kilovolts to a low load voltage is of great significance in various applications, but poses serious challenges. In this paper, a new converter, which is able to realize such a large step-down conversion in a single step, is proposed by introducing a novel concept of dc-dc multiphase conversion and n-phase interleaving rectification.
The proposed structure is formed by n switch pairs in the primary side, an n-phase isolation transformer with the primary windings connected to dc blocking capacitors, and an n-phase current multiplier in the output side. The switching patterns applied to the switch pairs have a phase difference of 360° mathord/ vphantom 360°n n, and the output inductor currents are interleaved correspondingly, making necessary a smaller output filter.
For a Vi input voltage and Io load current, the converter features Vi/n voltage stress on the primary-side switches, and Io/n current stress on the secondary-side inductors and diodes. Thus, the magnetic size of the inductors is considerable reduced. The primary-side switches are commutated with zero-voltage-switching (ZVS). Therefore, rather than using insulated-gate bipolar transistors (IGBTs) or MOSFETs with higher voltage ratings, the most available, notable performing 500/600 V MOSFETs can be used in the proposed converter with several kilovolts supply voltage, allowing for a higher operation frequency and lower conduction losses.
Compared with an input-series-output-parallel (ISOP) connection of full-bridge (FB) isolated converters, for the same voltage stress on the switches, the proposed converter requires half of the number of transistors and inherently balances the input voltage among the switch pairs. The switching mechanism of a typical switch pair in the kth interval Ts/n of a switching cycle is analyzed. A d- - c analysis was carried out to determine the dc conversion ratio and the ZVS conditions in an analytical form.
It allows for a tradeoff design of the converter, such that to minimize the duty-cycle loss and maximize the ZVS load range. A 1500/48-V, 2-kW prototype with four switch pairs was designed, implemented, and evaluated. The experimental results prove the soft switching of the switches, the low voltage stress across the primary-side switches, and the low current flowing through the rectifier's diodes and inductors. The efficiency measured at nominal power rating was 90.75%.
The proposed structure is formed by n switch pairs in the primary side, an n-phase isolation transformer with the primary windings connected to dc blocking capacitors, and an n-phase current multiplier in the output side. The switching patterns applied to the switch pairs have a phase difference of 360° mathord/ vphantom 360°n n, and the output inductor currents are interleaved correspondingly, making necessary a smaller output filter.
For a Vi input voltage and Io load current, the converter features Vi/n voltage stress on the primary-side switches, and Io/n current stress on the secondary-side inductors and diodes. Thus, the magnetic size of the inductors is considerable reduced. The primary-side switches are commutated with zero-voltage-switching (ZVS). Therefore, rather than using insulated-gate bipolar transistors (IGBTs) or MOSFETs with higher voltage ratings, the most available, notable performing 500/600 V MOSFETs can be used in the proposed converter with several kilovolts supply voltage, allowing for a higher operation frequency and lower conduction losses.
Compared with an input-series-output-parallel (ISOP) connection of full-bridge (FB) isolated converters, for the same voltage stress on the switches, the proposed converter requires half of the number of transistors and inherently balances the input voltage among the switch pairs. The switching mechanism of a typical switch pair in the kth interval Ts/n of a switching cycle is analyzed. A d- - c analysis was carried out to determine the dc conversion ratio and the ZVS conditions in an analytical form.
It allows for a tradeoff design of the converter, such that to minimize the duty-cycle loss and maximize the ZVS load range. A 1500/48-V, 2-kW prototype with four switch pairs was designed, implemented, and evaluated. The experimental results prove the soft switching of the switches, the low voltage stress across the primary-side switches, and the low current flowing through the rectifier's diodes and inductors. The efficiency measured at nominal power rating was 90.75%.
Space-Vector-Modulated Three-Level Inverters with a Single Z-Source Network
ABSTRACT
The Z-source inverter is a relatively recent converter topology that exhibits both voltage-buck and voltage-boost capability. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion whether two-level or multilevel. However, multilevel converters offer many benefits for higher power applications.
Previous publications have shown the control of a Z-source neutral point clamped inverter using the carrier-based modulation technique. This paper presents the control of a Z-source neutral point clamped inverter using the space vector modulation technique.
This gives a number of benefits, both in terms of implementation and harmonic performance. The adopted approach enables the operation of the Z-source arrangement to be optimized and implemented digitally without introducing any extra commutations. The proposed techniques are demonstrated both in simulation and through experimental results from a prototype converter.
Previous publications have shown the control of a Z-source neutral point clamped inverter using the carrier-based modulation technique. This paper presents the control of a Z-source neutral point clamped inverter using the space vector modulation technique.
This gives a number of benefits, both in terms of implementation and harmonic performance. The adopted approach enables the operation of the Z-source arrangement to be optimized and implemented digitally without introducing any extra commutations. The proposed techniques are demonstrated both in simulation and through experimental results from a prototype converter.
Synchronous-Reference-Frame-based Control of Switched Boost Inverter for Standalone DC Nanogrid Applications
ABSTRACT
Switched boost inverter (SBI) is a single-stage power converter derived from Inverse Watkins Johnson topology. Unlike the traditional buck-type voltage source inverter (VSI), the SBI can produce an ac output voltage that is either greater or less than the available dc input voltage.
Also, the SBI exhibits better electromagnetic interference noise immunity when compared to the VSI, which enables compact design of the power converter. Another advantage of SBI is that it can supply both dc and ac loads simultaneously from a single dc input. These features make the SBI suitable for dc nanogrid applications. In this paper, the SBI is proposed as a power electronic interface in dc nanogrid.
The structure and advantages of the proposed SBI-based nanogrid are discussed in detail. This paper also presents a dq synchronous-reference-frame-based controller for SBI, which regulates both dc and ac bus voltages of the nanogrid to their respective reference values under steady state as well as under dynamic load variation in the nanogrid.
The control system of SBI has been experimentally validated using a 0.5-kW laboratory prototype of the SBI supplying both dc and ac loads simultaneously, and the relevant experimental results are given in this paper. The low cross regulation and the dynamic performance of the control system have also been verified experimentally for a 20% step change in either dc or ac load of SBI.
These experimental results confirm the suitability of the SBI and its closed-loop control strategy for dc nanogrid applications.
Also, the SBI exhibits better electromagnetic interference noise immunity when compared to the VSI, which enables compact design of the power converter. Another advantage of SBI is that it can supply both dc and ac loads simultaneously from a single dc input. These features make the SBI suitable for dc nanogrid applications. In this paper, the SBI is proposed as a power electronic interface in dc nanogrid.
The structure and advantages of the proposed SBI-based nanogrid are discussed in detail. This paper also presents a dq synchronous-reference-frame-based controller for SBI, which regulates both dc and ac bus voltages of the nanogrid to their respective reference values under steady state as well as under dynamic load variation in the nanogrid.
The control system of SBI has been experimentally validated using a 0.5-kW laboratory prototype of the SBI supplying both dc and ac loads simultaneously, and the relevant experimental results are given in this paper. The low cross regulation and the dynamic performance of the control system have also been verified experimentally for a 20% step change in either dc or ac load of SBI.
These experimental results confirm the suitability of the SBI and its closed-loop control strategy for dc nanogrid applications.
Synthesizable Integrated Circuit and System Design for Solar Chargers
ABSTRACT
In this paper, an automatic design tool for a solar energy harvesting IC and system is developed with visual basic software, and the synthesis tool employed in this approach can be used to shorten the design time to market.
In addition, a smart meter system is developed to measure the solar energy harvesting system's information with an online system. Users can thus get the proposed system's information at any time and from anywhere. Finally, good agreement has been found between the analytic and experimental results.
In addition, a smart meter system is developed to measure the solar energy harvesting system's information with an online system. Users can thus get the proposed system's information at any time and from anywhere. Finally, good agreement has been found between the analytic and experimental results.
The Taipei Rectifier — A New Three-Phase Two-Switch ZVS PFC DCM Boost Rectifier
ABSTRACT
A new, three-phase, two-switch, power-factor-correction (PFC) rectifier that can achieve less than 5% input-current total harmonic distortion (THD) and features zero-voltage switching (ZVS) of all the switches over the entire input-voltage and load ranges is introduced.
The proposed rectifier also offers automatic voltage balancing across the two output capacitors connected in series, which makes it possible to use downstream converters designed with lower voltage-rated component that offer better performance and are less expensive than their high-voltage-rated counterparts.
In addition, the proposed rectifier also exhibits low common-mode EMI noise. The performance of the proposed rectifier was evaluated on a 2.8-kW prototype with a 780-V output that was designed to operate in 340-520-VL-L, RMS input-voltage range.
The proposed rectifier also offers automatic voltage balancing across the two output capacitors connected in series, which makes it possible to use downstream converters designed with lower voltage-rated component that offer better performance and are less expensive than their high-voltage-rated counterparts.
In addition, the proposed rectifier also exhibits low common-mode EMI noise. The performance of the proposed rectifier was evaluated on a 2.8-kW prototype with a 780-V output that was designed to operate in 340-520-VL-L, RMS input-voltage range.
Zero No-Load Power AC-DC Adapter for Electronic Equipment with Embed battery
ABSTRACT
A zero no-load power (ZNP) ac/dc adapter for electronic equipment with an embedded battery is proposed in this letter. The embedded battery is used as a signal source for the detection of load connection. Depending on the signal of load connection, an operation of the proposed ZNP ac/dc adapter is determined.
When the proposed adapter is connected with a load system, the operation of the proposed adapter is the same as that of the conventional ac/dc adapter. While the proposed adapter is disconnected from the load system, the overall proposed adapter is totally turned off.
Therefore, the proposed adapter can achieve ZNP consumption. To verify the validity of the proposed adapter, loss analysis and experimental results of 65 W are presented.
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When the proposed adapter is connected with a load system, the operation of the proposed adapter is the same as that of the conventional ac/dc adapter. While the proposed adapter is disconnected from the load system, the overall proposed adapter is totally turned off.
Therefore, the proposed adapter can achieve ZNP consumption. To verify the validity of the proposed adapter, loss analysis and experimental results of 65 W are presented.
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