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POWER ELECTRONICS 2017

Category Archives

Modified p-q Theory Based Control of Solar PV Integrated UPQC-S

Abstract:
This paper proposes a modified p-q theory based control of solar photovoltaic (PV) array integrated unified power quality conditioner (PV-UPQC-S). The system incorporates clean energy generation along with power quality improvement thus increasing functionality of the system. The fundamental frequency positive sequence (FFPS) components of voltages at the point of common coupling (PCC) are extracted using generalized cascaded delay signal cancellation (GCDSC) technique which are then used in p-q theory based control to estimate reference signals for the PV-UPQC-S. This modification in p-q theory enables its application for PV-UPQC-S control in conditions of distorted PCC voltages. The series voltage source converter (VSC) of PVUPQC- S operates such that it shares a part of the reactive power of the load even under nominal grid conditions. This increases the utilization of the series VSC while reducing the rating of shunt VSC. The PV array is integrated at the DC-bus of the UPQC, provides a part of active load power thus reducing demand on the supply system. The dynamic performance of modified p-q theory based PV-UPQC-S is verified by simulating the system in Matlab-Simulink with combination of linear and nonlinear loads. The steady state and dynamic performances of the system are then experimentally validated through extensive testing on a scaled down laboratory prototype.


A Transformer-less Unified Power Quality Conditioner with Fast Dynamic Control

Abstract:
A single-phase transformer-less unified power quality conditioner (TL-UPQC) is presented. Apart from having no isolation transformer, the proposed structure utilizes four switching devices only, forming two half-bridge voltage-source inverters – one connected in parallel with the load and another one connected in series with the AC mains. The two inverters share the same DC link. The parallel inverter, which is controlled by a hysteresis current controller, is used to shape the current drawn from the AC mains and regulate the DC-link voltage. The series inverter, which is controlled by a boundary controller with second-order switching surface, is used to regulate the steady-state load voltage and provide voltage sag / swell ride-through. A DC-link capacitor voltage balancing control that coordinates the operations of the hysteresis and boundary controllers is designed. Modeling, design, and analysis of the whole system will be given. A 1kVA, 110V, 60Hz prototype has been built and evaluated on a setup with a nonlinear load. The steady-state and transient responses under a voltage sag will be given. Experimental results are favorably compared with the theoretical predictions and the performance of other UPQCs.


Power Control with Z-Source Converter based Unified Power Flow Controller

Abstract:
In this paper, we propose a Z-Source Converter (ZSC) based Unified Power Flow Controller (ZSCUPFC) to enhance power control for long transmission lines. As a multi-functional controller, the unified power flow controller (UPFC) has been adopted to regulate both the active and reactive power flows in transmission lines and to control the AC bus voltage. A recently proposed converter topology, ZSC, uses a Z-network on its DC side to support the desired AC output voltage. The proposed ZSC-UPFC configuration places a Z-network between the DC link capacitor and the series converter to boost the series converter DC voltage. The integration of Z-network provides the desired converter voltage even with reduced DC link capacitor voltage setting. We develop a detailed three-phase model for the proposed ZSC-UPFC by modeling the converter operation with switching functions, which are generated by the Space Vector Pulse Width Modulation (SVPWM) technique. We conduct linear analysis on D-Q model as well as extensive transient simulation (based on a detailed nonlinear three-phase model) to evaluate the performance of the overall system with the proposed ZSC-UPFC configuration. Our simulation results demonstrate the effectiveness of ZSC-UPFC: i) the series converter provides the series compensation in a long transmission line with Z-network, and ii) the shunt converter maintains a constant DC link capacitor voltage and provides reactive power support for the AC bus.


Fuzzy Logic Based UPFC and Laboratory Prototype Validation for Dynamic Power Flow Control in Transmission Lines

Abstract:
In this paper, Fuzzy Logic Controller (FLC) is proposed to overcome the problems of the existing UPFC controllers and to provide the dynamic power flow control through transmission lines. Although many researches have been focusing on developing UPFC control strategies for power flow control through simulation, there is a lack of experimental validation of different UPFC controllers and its performance in real time operation. In order to investigate the performance of the proposed FLC based UPFC, a laboratory prototype has been developed using two 6-pulse converters. The shunt and series controller for both PI and FLC based UPFC prototype are designed in MATLAB/SIMULINK® using Speedgoat® performance real time target machine. The UPFC prototype is tested on 6 – bus power system network model to verify its capability. The results revealed that the UPFC prototype had successfully controlled power flow dynamically in transmission line with enhanced accuracy. In addition, other power system parameters have been improved significantly.


Clustered Voltage Balancing Mechanism and its Control Strategy for Star-Connected Cascaded H-Bridge STATCOM

Abstract:
To explore the clustered voltage balancing mechanism of the Star-connected Cascaded H-Bridge (SCHB) STATCOM, this paper analyses the relationship between the active power and the control variables – modulation reference voltages in dq frame through positive and negative sequence component decomposition. The derived relationship in dq frame reveals that the negative sequence modulation reference voltage is capable of redistributing the active power among three phases and also the SCHB STATCOM features the clustered voltage self-stabilizing without any additional clustered voltage balancing control. To eliminate the differences of three clustered voltages, a new clustered voltage balancing control is proposed by regulating negative sequence modulation reference voltage in dq frame. Its balancing mechanism is analyzed in detail and a simple implementation is presented as well. The effectiveness of the proposed control is verified by experimental results on a 400V/15kVar SCHB STATCOM.


Sensitive Load Voltage Compensation Performed by a Suitable Control Method

Abstract:
This work proposes the usage of a repetitive-based control to dynamically restore the voltage applied to sensitive and critical loads of power system. The control intrinsically is able to wipe off harmonic distortion and relies on simple transfer function. As a consequence, there is no need to apply harmonic selective filters. Furthermore, the control system is able to work out on sinusoid references and, thus, avoids the need of employing the dq transform. A recursive least-squares is also included to the control system in order to assure the synchronization of the voltages to be restored. The design of the control parameters along with the system stability are discussed. The experimental results are produced with a setup of a three-phase series compensator. The scenarios for emulating faulty voltages are the same for experimental and simulated results. The results corroborates the usage of the proposed method.


Photovoltaic Module-Integrated Stand-alone Single-Stage Switched Capacitor Inverter with Maximum Power Point Tracking

Abstract:
A switched capacitor (SC) based inverter that tracks the maximum power point (MPP) of a photovoltaic (PV) source and generates a pure sine output is presented. To enable integration with the PV module, efficiency and compactness are maximized with a single-stage topology that tracks the MPP of the PV source, boosts the input dc voltage, and generates a regulated ac output in a stand-alone configuration with scope for grid-connected applications. The SC inverter is realized with multiple identical SC blocks controlled by sinusoidal pulsewidth modulation and load-dependent output capacitor adjustment. A detailed steady-state analysis is carried out, and a mathematical model is derived to understand the interdependence of various inverter parameters on each other and to optimally choose the inverter components. A hardware prototype of the stand-alone single-stage SC inverter that operates from a 60 V/70 W PV module and delivers a 110 Vrms, 50 Hz output is wired to demonstrate the functioning of the proposed MPP tracking inverter under different operating conditions. An inversion efficiency > 95%, a tracking efficiency > 97%, and a total harmonic distortion (THD) <; 4% have been practically achieved. All the details of this work are presented.


Photovoltaic Module-Integrated Stand-alone Single-Stage Switched Capacitor Inverter with Maximum Power Point Tracking

Abstract:
A switched capacitor (SC) based inverter that tracks the maximum power point (MPP) of a photovoltaic (PV) source and generates a pure sine output is presented. To enable integration with the PV module, efficiency and compactness are maximized with a single-stage topology that tracks the MPP of the PV source, boosts the input dc voltage, and generates a regulated ac output in a stand-alone configuration with scope for grid-connected applications. The SC inverter is realized with multiple identical SC blocks controlled by sinusoidal pulsewidth modulation and load-dependent output capacitor adjustment. A detailed steady-state analysis is carried out, and a mathematical model is derived to understand the interdependence of various inverter parameters on each other and to optimally choose the inverter components. A hardware prototype of the stand-alone single-stage SC inverter that operates from a 60 V/70 W PV module and delivers a 110 Vrms, 50 Hz output is wired to demonstrate the functioning of the proposed MPP tracking inverter under different operating conditions. An inversion efficiency > 95%, a tracking efficiency > 97%, and a total harmonic distortion (THD) <; 4% have been practically achieved. All the details of this work are presented.


Voltage THD Reduction for Dual-Inverter Fed Open-End Load With Isolated DC Sources

Abstract:
In this paper, the near-state pulse width modulation (NSPWM), adapted to be used in dual-voltage source inverter (VSI) fed open-end load, is introduced primarily aiming to appreciably minimize the voltage total harmonic distortion (THD). Within the framework of the proposed method, the active time of pulses at the second inverter is relatively adjusted within switching interval (compared to the first VSI). The phase voltage harmonics are formulated for dual-inverter modulated by NSPWM; then, optimal adjustment is identified via a three-dimensional curve of phase voltage THD versus modulation index (MI) and phase angle displacement (PAD). Due to the limitation of MI in NSPWM, the desired output voltage is synthesized with modifying not only MI but also PAD between references of two VSIs. Furthermore, NSPWM inherently takes advantage of better efficiency compared to conventional space vector modulation due to switching only two phases within an interval (by clamping one phase to positive/negative dc-rail). The dual-VSI supplied by two isolated dc sources is assembled in the laboratory to experimentally evaluate the THD reduction feature of the proposed method; also, the simulation results obtained by means of a MATLAB/Simulink environment show close agreement with experimental data.


ZVS Phase-Shift PWM-Controlled Single-Stage Boost Full-Bridge AC–AC Converter for High-Frequency Induction Heating Applications

Abstract:
This paper presents a new single-stage utility frequency ac-high-frequency ac resonant power converter for high-frequency induction heating applications. The newly proposed ac-ac converter features a boost converter and a full-bridge resonant inverter integrated circuit with a source voltage sensorless control system. The experimental results of a 3.0 kW-40 kHz prototype are demonstrated on zero-voltage soft switching and steady-state characteristics, then, the validity of the proposed ac-ac converter is revealed from a practical viewpoint.


A Highly Reliable and High-Efficiency Quasi Single-Stage Buck–Boost Inverter

Abstract:
To regulate an output ac voltage in inverter systems having wide input dc voltage variation, a buck-boost power conditioning system is preferred. This paper proposes a novel high-efficiency quasi single-stage single-phase buck-boost inverter. The proposed inverter can solve current shoot-through problem and eliminate PWM dead time, which leads to greatly enhanced system reliability. It allows bidirectional power flow and can use MOSFET as switching device without body diode conducting. The reverse recovery issues and related loss of the MOSFET body diode can be eliminated. The use of MOSFET contributes to the reduction of switching and conduction losses. Also, the proposed inverter can be operated with simple pulse width modulation (PWM) control and can be designed at higher switching frequency to reduce the volume of passive components. The detailed experimental results are provided to show the advantages of the proposed inverter. Efficiency measurement shows that using simple PWM control the proposed inverter can obtain peak efficiency of 97.8% for 1.1-kW output power at 30-kHz switching frequency.


An experimental study of modified space vector modulation applied to quasi Z source inverters using FPGA

Abstract:
Z-source/quasi Z-source inverters (qZSI) can eliminate DC-DC converter in conventional drive applications where DC-DC converter is coupled with voltage source inverter (VSI). Compared to Z-source inverter (ZSI), qZSI has more advantages like continuous input current and lower component ratings. In these inverters, DC link voltage is boosted by using shoot through state i.e., turning ON both the switches in the inverter leg. In this paper, conventional space vector modulation is modified for introducing shoot through state that is necessary for boosting DC link voltage, without any extra switching operations. This paper gives detailed implementation steps for this modified space vector modulation and is implemented by FPGA.


A Superconducting Magnetic Energy Storage-Emulator/Battery Supported Dynamic Voltage Restorer

Abstract:
This study examines the use of superconducting magnetic and battery hybrid energy storage to compensate grid voltage fluctuations. The superconducting magnetic energy storage system (SMES) has been emulated by a high-current inductor to investigate a system employing both SMES and battery energy storage experimentally. The design of the laboratory prototype is described in detail, which consists of a series-connected three phase voltage source inverter used to regulate ac voltage, and two bidirectional dc/dc converters used to control energy storage system charge and discharge. “DC bus level signaling” and “voltage droop control” have been used to automatically control power from the magnetic energy storage system during short-duration, high-power voltage sags, while the battery is used to provide power during longer term, low-power undervoltages. Energy storage system hybridization is shown to be advantageous by reducing battery peak power demand compared with a battery-only system, and by improving long-term voltage support capability compared with an SMES-only system. Consequently, the SMES/battery hybrid dynamic voltage restorer can support both short-term high-power voltage sags and long-term undervoltages with significantly reduced superconducting material cost compared with an SMES-based system.


Direct Model Predictive Current Control Strategy of Quasi-Z-Source Inverters

Abstract:
This paper presents a direct model predictive current control (MPC) strategy for quasi-Z-source inverters (qZSIs). A discrete-time model is derived that accurately captures all operating modes of the converter. Both sides of the qZSI are controlled simultaneously based on the inductor current and capacitor voltage on the dc side as well as the output current on the ac side. To improve the closed-loop performance of the converter, a long prediction horizon is implemented. However, the underlying optimization problem may become computationally intractable because of the substantial increase in the computational power demands, which in turn would prevent the implementation of the control strategy in real time. To overcome this and to solve the problem in a computationally efficient manner, a branch-and-bound strategy is used along with a move blocking scheme. Simulation and experimental results are provided to verify the effectiveness of the presented control strategy.


A New Single-Phase Switched-Coupled-Inductor DC–AC Inverter for Photovoltaic Systems

Abstract:
This paper presents a new single-phase switched-coupled-inductor dc-ac inverter featuring higher voltage gain than the existing single-phase qZ-source and semi-Z-source inverters. Similar to the single-phase qZ-source and semi-Z-source inverters, the proposed inverter also has common grounds between the dc input and ac output voltages, which is beneficial especially for photovoltaic inverter systems. The inverter volume and maximum current flowing can be reduced significantly through the coupling of all inductors. A theoretical analysis of the proposed inverter is described and a 280-W experimental prototype is built to verify the performance of the inverter.


Model-Based Active Damping Control for Three-Phase Voltage Source Inverters With LCL Filter

Abstract:
This paper presents a robust model-based active damping control in natural frame for a three-phase voltage source inverter with LCL filter. The presence of the LCL filter complicates the design of the control scheme, particularly when system parameters deviation is considered. The proposed control method is addressed to overcome such difficulties and uses a modified converter model in a state observer. In this proposal, the converter model is modified by introducing a virtual damping resistor. Then, a Kalman filter makes use of this model to estimate the system state-space variables. Although the state estimates do not obviously match the real world system variables, they permit designing three-current sliding-mode controllers that provide the following features to the closed loop system: 1) robust and active damping capability like in the case of using a physical damping resistor; 2) robustness because the control specifications are met independently of variation in the system parameters; 3) noise immunity due to the application of the Kalman filter; and 4) power loss minimization because the system losses caused by the physical damping resistor are avoided. An interesting side effect of the proposed control scheme is that the sliding surfaces for each controller are independent. This decoupling property for the three controllers allows using a fixed switching frequency algorithm that ensures perfect current control. To complete the control scheme, a theoretical stability analysis is developed. Finally, selected experimental results validate the proposed control strategy and permit illustrating all its appealing features.


Wide Input-Voltage Range Boost Three-Level DC–DC Converter With Quasi-Z Source for Fuel Cell Vehicles

Abstract:
To solve the problem of the mismatched voltage levels between the dynamic lower voltage of the fuel cell stack and the required constant higher voltage (400 V) of the dc-link bus of the inverter for fuel cell vehicles, a boost three-level dc-dc converter with a diode rectification quasi-Z source (BTL-DRqZ) is presented in this paper, based on the conventional flying-capacitor boost three-level dc-dc converter. The operating principle of a wide range voltage-gain for this topology is discussed according to the effective switching states of the converter and the multiloop energy communication characteristic of the DRqZ source. The relationship between the quasi-Z source net capacitor voltages, the modulation index, and the output voltage is deduced and then the static and dynamic self-balance principle of the flying-capacitor voltage is presented. Furthermore, a boost three-level dc-dc converter with a synchronous rectification quasi-Z source (BTL-SRqZ) is additionally proposed to improve the conversion efficiency. Finally, a scale-down 1.2 kW BTL-SRqZ prototype has been created, and the maximum efficiency is improved up to 95.66% by using synchronous rectification. The experimental results validate the feasibility of the proposed topology and the correctness of its operating principles. It is suitable for the fuel cell vehicles.


A Three-Level LC-Switching-Based Voltage Boost NPC Inverter

Abstract:
A single-stage high-voltage gain boost inverter is getting popularity in applications like solar photovoltaic, fuel cell, uninterruptible power system (UPS) systems, etc. Recently, single-stage voltage boost multilevel Z-source inverter (ZSI) and quasi-Z-source inverter (QZSI) have been proposed for dc-ac power conversion with improved power quality. Multilevel ZSI uses more number of high-power passive components in the intermediate network, which increase the system size and weight. Also, its input current is discontinuous in nature which is not desirable in some of the applications like fuel cell, UPS systems, hybrid electric vehicle, etc. In this paper, a continuous current input three-level LC-switching-based voltage boost neutral-point-clamped inverter is proposed, which uses comparatively less number of high-power passive components at the same time retains all the advantages of multilevel QZSI/ZSI. It is able to boost the input dc voltage and give required three-level ac output voltage in a single stage. Steady-state analysis of the proposed inverter is discussed to formulate the relationship between the input dc voltage and three-level ac output voltage. A unipolar pulse width modulation technique devised for the proposed inverter to eliminate first center band harmonics is also presented. The proposed converter has been verified by simulation in MATLAB Simulink as well as performing experiment with the help of a laboratory prototype.


Stability Analysis and Controller Synthesis for Single-Loop Voltage-Controlled VSIs

Abstract:
This paper analyzes the stability of digitally voltage-controlled voltage-source inverters (VSIs) with the linear voltage regulators. It is revealed that the phase lags, caused by using the resonant controller and the time delay of a digital control system, can stabilize the single-loop voltage control without damping of the LC -filter resonance. The stability region for the digital single-loop resonant voltage control is then identified, considering the effects of different discretization methods for the resonant controller. An enhanced voltage control approach with a widened stability region is subsequently proposed, and a step-by-step design method of the proposed controller is developed based on the root contours in the discrete z-domain. Simulations and experimental tests of a 400-Hz VSI system validate the stability analysis and the performance of the proposed control approach.


Single-Stage Three-Phase Current-Source Photovoltaic Grid-Connected Inverter High Voltage Transmission Ratio

Abstract:
This paper proposes a circuit topology of a single-stage three-phase current-source photovoltaic (PV) grid-connected inverter with high voltage transmission ratio (VTR). Also, an improved zone sinusoidal pulsewidth modulation (SPWM) control strategy and an active-clamped subcircuit that can suppress the energy storage switch’s turn-off voltage spike are introduced. The circuit topology, control strategy, steady principle characteristics, and high-frequency switching process are analyzed profoundly, as well as the VTR’s expression and design criterion of the center-tapped energy storage inductor. The improved zone SPWM control strategy consists of two control loops, namely, the outer loop of input dc voltage of PV cells with the maximum power point tracking and the inner loop of the energy storage inductor current. The experimental results of a 3-kW 96VDC/380V50Hz3ϕAC prototype have shown that this kind of a three-phase inverter has the excellent performances such as single-stage power conversion, high VTR and power density, and high conversion efficiency. Nonetheless, it has small energy storage inductor and output CL filter, low output current total harmonic distortion, and flexible voltage configuration of the PV cells. This study provides an effective design method for single-stage three-phase inverting with high VTR.


Current Ripple Damping Control to Minimize Impedance Network for Single-Phase Quasi-Z Source Inverter System

Abstract:
The single-phase quasi-Z source inverter (qZSI) topology has recently attracted attention for single-phase grid-tie photovoltaic (PV) applications. However, due to the inherent second-harmonic power flow in single-phase systems, a large qZS network is required to reduce the second-harmonic component of currents and voltages on the dc side. Minimization of the qZS network remains an open issue. This paper proposes a technique that minimizes the qZS capacitance and inductance of the single-phase qZSI topology by employing dc-side low-frequency current ripple damping control. Through analysis of power flow, a second-harmonic power model is derived and the ripple power is analyzed for minimization of the qZS network. A current ripple damping control is proposed to ensure suppression of second-harmonic power flow through the inductors. Simulation and experimental results verify the theoretical analysis, damping control, and the proposed design minimization of the qZS network for the single-phase topology.


Hybrid Pulsewidth Modulated Single-Phase Quasi-Z-Source Grid-Tie Photovoltaic Power System

Abstract:
A hybrid pulsewidth modulated single-phase quasi-Z-source grid-tie photovoltaic (PV) power system is proposed. The hybrid pulse-width modulation (HPWM) combines the pulse-width modulation (PWM) and the pulse-amplitude modulation (PAM). The PWM works when the ac output voltage is lower than the dc source voltage; otherwise, the PAM operates the single-phase quasi-Z-source inverter (qZSI). The HPWM leads to the reduction of power loss, and the quasi-Z-source capacitance and inductance. An effective control strategy is proposed for the new PV power system to manage the maximum power point tracking (MPPT) of PV panel, grid-tie power injection, and dc-link voltage. A grid-tie current controller, combining a repetitive controller and a proportional-resonant regulator, achieves strong harmonic suppression, fast dynamic, and zero tracking error. A 500-W prototype is built to verify the new system. Power loss estimation and impedance design are detailed. Experimental tests validate the HPWM, new PV power system with higher efficiency, and the related control method.


Quasi-Z-Source Network-Based Hybrid Power Supply System for Aluminum Electrolysis Industry

Abstract:
A hybrid power supply system (HPSS) based on the quasi-Z-source network is proposed for aluminum electrolysis, which can reduce energy consuming and carbon emission through the use of renewable energy. An ac-dc integrate controller is designed in the HPSS that contains a two-layer control. The first layer control is responsible for maintaining the dc bus voltage and current, which can mitigate negative effects caused by anode effect in aluminum electrolysis. The independent maximum power tracking for PV array and the dc-bus voltage balance for each quasi-Z-source dc-dc converter can be achieved by using the PV-voltage controller and dc-bus voltage controller for the PV System. To maintain the voltage of dc bus within the require voltage range of aluminum electrolysis production and ensure high input power quality of ac System, the quasi-Z-rectifier controller is employed, which can reduce the harmonic injection. The power allocation is addressed in the second control layer and a power scheme algorithm (PSA) is carried out to maximize the system efficiency and economic benefit. At last, the simulation and experimental results are provided to verify the effectiveness of the designed HPSS and the proposed PSA.


Design and Steady-State Analysis of Parallel Resonant DC–DC Converter for High-Voltage Power Generator

Abstract:
A novel voltage-doubling circuit with parallel-resonant dc-dc converter is proposed. The converter consists of full-bridge inverter, resonant tank, high-frequency high-voltage transformer, and voltage-doubling circuit. In the high-voltage applications, low-output voltage ripple has been given much attention. The output voltage step-up ratio is increased by two parts. One is a high-frequency high-voltage transformer and the other is a voltage-doubling circuit. The novel voltage-doubling circuit can not only reach a higher output voltage but also reduce output ripple to a lower level than the conventional one. Therefore, while maintaining the same output voltage, the transformer’s turn ratio can be reduced compared with the conventional voltage-doubling circuit. The output power can be adjusted by the phase-shift control technique. In addition, combining this technique with the parallel resonant tank can make all the switches achieve zero voltage turn on (ZVS). The operating principles, steady-state analysis, and the parameter designs are discussed in this paper. Finally, a prototype circuit with 400-V input voltage, 40-kV output voltage, and 300-W output power is developed in the laboratory to verify the performance of the proposed converter.


A Fault-Tolerant Series-Resonant DC–DC Converter View Document

Abstract:
The series-resonant dc-dc converter (SRC) is widely used as power supply for telecommunications, wireless power transfer for electrical vehicle, and high-voltage power supplies. Recently, it became very popular in solid-state transformer application, where fault tolerance is a highly desired feature and it is obtained through redundancy. This letter proposes a reconfiguration scheme for the SRC for the case of failure in one semiconductor, which could drastically reduce the need of redundancy. Using the proposed scheme, the full-bridge based SRC can be reconfigured in a half-bridge topology, in order to keep the converter operational even with the failure [open circuit (OC) or short circuit (SC)] of one switch. As a drawback of this technique, the output voltage drops to half of its original value. Therefore, a novel reconfigurable rectifier based on the voltage-doubler topology is proposed as a solution to keep the output voltage constant after the fault. To verify the feasibility of the proposed scheme, the converter is tested experimentally in a 700-600 V prototype with 10 kW of output power. An insulated gate bipolar transistor (IGBT) SC fault is tested and the results confirm the effectiveness of the proposed approach.


A DC-Voltage-Controlled Variable Capacitor for Stabilizing the ZVS Frequency of a Resonant Converter for Wireless Power Transfer

Abstract:
Varactors are often used in phase-locked-loop (PLL) circuits for dynamic frequency control. However, the voltage and current ratings of varactors are too low to be used in most power electronic circuits. This paper proposes a transistor-controlled variable capacitor (TCVC), which functions similar to varactors in that its equivalent capacitance can be controlled by a dc voltage. However, TCVC can handle high voltages and currents so that it can be used in dc-ac power converters of wireless power transfer (WPT) systems such as an autonomous push-pull resonant converter to adjust its zero voltage switching (ZVS) frequency so that the operating frequency of the system can be stabilized to simplify the circuit and EMI filter design particularly for WPT systems with multiple power pickups while maintaining soft-switching operation of the converter against magnetic coupling and load variations. The relationship between the equivalent capacitance of the TCVC and the dc control voltage is developed by theoretical analysis and verified by experimental results. A prototype circuit is built with a PLL controller to demonstrate that the soft-switching condition of the converter is maintained when the operating frequency is locked in at 1.65 MHz under load and magnetic coupling variations.


Active Suppression of Selected DC Bus Harmonics for Dual Active Bridge DC–DC Converters

Abstract:
AC coupled dual active bridge (DAB) dc-dc converters typically use phase shifted square wave (PSSW) modulation to manage the power flow between two dc sources. With this scheme, the current flowing between the converter bridges injects high-magnitude current harmonics into each dc port at multiples of the primary switching frequency, which can excite resonances in the LC circuits created by parasitic second-order impedances such as wiring inductances in the dc-link connections. This can cause substantial dc bus voltage and current oscillations, particularly with the higher switching frequencies that are used with wide bandgap devices, leading to excessive electromagnetic interference, significant filter stress, and eventual component operational failure. Conventionally, a relatively large dc bus filter capacitor (or inductor) helps to suppress these dc bus harmonic dynamics. However, the use of adaptive three-level modulation for a single phase DAB provides a much greater solution space to achieve a desired power transfer condition, with the three PSSW control angles that are available. This paper now explores the additional use of these angles to selectively suppress particular dc bus current harmonics across the entire operating range of the converter and thus allow the size of the DAB dc bus bridge capacitors to be minimized. This new active harmonic suppression (AHS) strategy is validated by theory, simulation, and matching experimental results.


A Full Soft-Switching ZVZCS Flyback Converter Using an Active Auxiliary Cell

Abstract:
In this paper, a new soft switching flyback dc-dc converter with a simple zero-voltage and zero-current switching (ZVZCS) cell is proposed. The auxiliary resonant cell consists of one switch, one diode, one inductor, and two capacitors. It provides ZVZCS not only for the main switch but also for the auxiliary switch at both turn-on and turn-off times. In addition, all the auxiliary diodes and body diodes of the switches operate under full ZVZCS except the output diode which turns off only with zero current switching. This soft switching technique makes the proposed converter have less switching losses which leads the converter to operate in higher frequencies and efficiency. Another outstanding feature of the proposed converter is using the auxiliary resonant cell out of the main power path to have lower voltage stress on the switches. In this paper, pulse width modulation (PWM) is employed to control the main switch. A detailed mode analysis of the proposed converter operation is presented along with design procedure. Finally, the accuracy performance of the converter is verified through a 60 W experimental prototype results.


Dead Time Effect on the Double-Loop Control Strategy for a Boost Inverter

Abstract:
The boost inverter topology achieves both boosting and inversion in a single stage. Various controllers have been implemented on boost inverters to obtain stable operation. However, the double-loop control strategy is the most appropriate because it provides good performance under nonlinear loads, abrupt load variations, and transient short-circuit conditions. The double-loop control strategy was introduced with proportional integral (PI) controllers used in each loop. Recently, with the widespread use of proportional resonant (PR) controllers, the PI controllers were replaced with the PR controllers to achieve zero steady-state error for the ac components of the reference. However, during the implementation of the PR controllers, a significant dc offset in the output voltage of the boost inverter was observed. Furthermore, the output voltages of the boost converters showed a clipping effect. In this paper, it is shown that the dc offset and the clipping of the boost converters are attributed to the dead time and parameter mismatch between the boost converters. A new controller is proposed to reduce the dc offset and clipping effect. The improved performance of the proposed controller is demonstrated with experimental results on a boost inverter prototype.


An Average Input Current Sensing Method of LLC Resonant Converters for Automatic Burst Mode Control

Abstract:
Burst mode control techniques have been studied for LLC resonant dc-dc converters to improve power conversion efficiencies at light load conditions. However, there are not many studies about how to detect the load conditions at burst mode not even at normal mode, at the primary side of LLC resonant dc-dc converters. In this paper, we propose and implement a lossless load detection technique for normal and burst modes by a novel average input current sensing method at the primary side of LLC resonant converters. Detailed theoretical analysis at normal and burst modes is presented and a load detection circuit is proposed with the consideration of integrated circuits. To verify the analysis, an LLC resonant offline converter with 400 V input and 16 V/10 A output is simulated using PSIM and a prototype board is built. The experimental results show that the proposed load detection technique is valid and practical. As a result, an automatic burst mode control for LLC resonant converters at light load conditions is realized with the proposed average input current sensing method.


A Family of High-Frequency Single-Switch DC–DC Converters With Low Switch Voltage Stress Based on Impedance Networks

Abstract:
This paper presents a novel family of single-switch resonant dc-dc converters with low switch voltage stress. The single-switch resonant converter which has a ground-referenced switch is advantageous for implementing the gate drive circuit and operating at several-MHz switching frequency. However, the conventional ones mostly have high voltage stress on the switch, roughly 4-5 times the input voltage. In this paper, we propose the single-switch converter topologies derived from the drain-source impedance networks consisting of two inductors and two capacitors. The switch voltage of the proposed converters is shaped into a near trapezoid by designing the resonant networks to have the desired drain-source impedance. Furthermore, a simple and specific design scheme is presented here so that the peak switch voltage is lowered to 2.2-2.5 times the input voltage while zero voltage switching is achieved. Experimental results from a 20-W GaN-based prototype operating at 10 MHz demonstrate the feasibility of the proposed converter topologies and the design method.


Analysis, Design, and Experimentation of a Dimmable Resonant-Switched-Capacitor LED Driver With Variable Inductor Control

Abstract:
This paper proposes a new 48-V dc-fed dimmable LED driver based on a resonant-switched-capacitor topology (RSCT), where the analog-based dimming feature is accomplished by means of a variable inductor (VI). The proposed topology is based on the classic RSCT step-up double mode converter and it provides a simple and cost-effective solution while guaranteeing a wide dimming range. In order to implement an analog-based dimming, the control of the dc current in the LED lamp is required. This technique proposes to replace the resonant inductor by a VI, which will control the rms value of the resonant current, and, therefore, the mean value of the LED lamp current. In order to evaluate the feasibility and performance of this method, a 22-W LED lamp and driver prototypes were built. The most relevant experimental results are presented and briefly described.


A Digital Current Control Technique for Grid-Connected AC/DC Converters Used for Energy Storage Systems

Abstract:
This paper presents an advanced current controller for grid-connected bidirectional ac/dc converters used for energy storage systems (ESSs). The proposed control scheme is designed to incorporate both the time-domain and frequency-domain dynamics to achieve superior transient and steady-state performance. The advanced current controller can overcome the various challenges faced by the conventional current controllers used in this application, which lead to sluggish transients and steady-state errors when tracking the sinusoidal reference for the grid current. Combining the time-domain dynamics with the frequency-domain dynamics creates a more intelligent controller compared to existing methods, which only consider the dynamics of one domain. The proposed controller is able to eliminate steady-state error by adaptively changing the controller coefficients in the frequency domain according to the current error. In the time domain, the control scheme minimizes the derivative of a defined energy function in order to optimize the transient performance. Simulation and experimental results obtained from a 3.3-kW grid-connected ac/dc converter demonstrate its superior performance.


Single-Switch High-Frequency DC–DC Converter Using Parasitic Components

Abstract:
This paper presents a single-switch isolated dc-dc converter suited for a very high-frequency switching operation, especially above 10 MHz. The converter features a small number of passive components, low-switching loss, and low-voltage stress on the switch. In order to achieve low-voltage stress while maintaining zero voltage switching, the voltage waveform across the switch is shaped by designing the resonant network of the converter. The resonant network includes main parasitic components, such as leakage inductances of the transformer and the junction capacitance of the switch. Furthermore, some resonant elements are entirely replaced by these parasitic components under the specific condition. This paper derives the conditions and then minimizes the number of passive components. To validate the design procedure and the performance of the proposed converter, a GaN-based prototype was implemented. It operates at 10 MHz and provides the output power of 10 W from the dc input voltage of 50 V. The output voltage is regulated to 20 V by the ON-OFF control. Experimental results show that the peak voltage on the switch is reduced to 2.2-2.3 times the dc-input voltage and the efficiency of 69% is achieved under the full load.


A Dual Series-Resonant DC–DC Converter

Abstract:
A dual series-resonant dc-dc converter with zero-voltage switching and zero-current switching features is proposed in this paper. The topology consists of two switches and a clamping capacitor on the primary side of an isolating transformer. The two switches are operated in a complementary mode under a pulse width modulation (PWM) scheme. The secondary side of the transformer is connected to the load through two series-resonant circuits and a half-bridge diode rectifying stage, in which the rise and fall slopes of the diode currents are limited by the slope of the currents in the resonant circuits, resulting in reduced switching losses in the diodes. The two series-resonant circuits provide power transfer to the output load without interruption throughout the positive and negative cycles of operation. It is shown that the output voltage of the proposed converter can be regulated using either PWM control or frequency modulation control. Both step-down and step-up voltage conversions can be achieved using the proposed topology. Programmable system-on-chip is used as the controller platform to implement a 40 W laboratory prototype. A complete steady-state analysis is presented and the experimental results of the prototype of the proposed converter are discussed.


Low-Frequency DC-Link Ripple Elimination in Power Converters With Reduced Capacitance by Multiresonant Direct Voltage Regulation

Abstract:
In this paper, a method for suppressing the low-frequency portion of dc-link ripple inevitably present in power conversion systems with reduced capacitance is proposed. The discussed active capacitance reduction circuitry (consisting of a feedback-controlled shunt-connected bidirectional buck-boost converter, terminated by a small auxiliary capacitance) directly regulates the dc-link voltage, utilizing a dual-loop control structure with parallel-connected multiresonant-bank-enhanced voltage loop stabilizing controller to achieve nearly constant, low-frequency-ripple-free steady-state dc-link voltage. Consequently, the proposed active capacitance reduction system may be perceived as a virtual infinite capacitor from the dc link point of view. The suggested circuitry is successfully applied to a single-phase commercial power factor correction front end in a nearly plug-and-play fashion. The control algorithm effectiveness is fully supported by simulations and experimental results.


An Integrated Battery Charger With High Power Density and Efficiency for Electric Vehicles

Abstract:
Power conversion systems for electric vehicles (EVs) have been researched to improve power density and efficiency at low cost. To satisfy these needs for EVs, this paper proposes a novel battery charging system that integrates a nonisolated on-board charger (OBC) and low-voltage dc-dc converters (LDCs) by sharing the semiconductor devices and mechanical elements. Thus, the volume of LDCs is reduced dramatically compared with a conventional nonintegrated charging system. The proposed integrated system is configured based on a driving condition that is derived from the analysis of vehicle operating modes. In order to improve system’s performance, an asynchronous control algorithm is applied to control the OBC optimally. In the LDC system, two LLC resonant converters are composed by sharing a transformer and secondary-side components. To increase the efficiency of each LDC, which is operated in the wide input and output voltage range, a duty and frequency control algorithm is proposed. The theoretical analysis, operating strategy, and experimental results on a 6.6-kW OBC and 1.9-kW LDC are presented to evaluate the performance of the proposed system; the total volume of LDCs is 1.87 L, and peak efficiencies of OBC and LDC are 97.3% and 93.13%, respectively. Moreover, a comparative analysis is presented to evaluate the performance of the proposed system.


An Integrated Battery Charger With High Power Density and Efficiency for Electric Vehicles

Abstract:
Power conversion systems for electric vehicles (EVs) have been researched to improve power density and efficiency at low cost. To satisfy these needs for EVs, this paper proposes a novel battery charging system that integrates a nonisolated on-board charger (OBC) and low-voltage dc-dc converters (LDCs) by sharing the semiconductor devices and mechanical elements. Thus, the volume of LDCs is reduced dramatically compared with a conventional nonintegrated charging system. The proposed integrated system is configured based on a driving condition that is derived from the analysis of vehicle operating modes. In order to improve system’s performance, an asynchronous control algorithm is applied to control the OBC optimally. In the LDC system, two LLC resonant converters are composed by sharing a transformer and secondary-side components. To increase the efficiency of each LDC, which is operated in the wide input and output voltage range, a duty and frequency control algorithm is proposed. The theoretical analysis, operating strategy, and experimental results on a 6.6-kW OBC and 1.9-kW LDC are presented to evaluate the performance of the proposed system; the total volume of LDCs is 1.87 L, and peak efficiencies of OBC and LDC are 97.3% and 93.13%, respectively. Moreover, a comparative analysis is presented to evaluate the performance of the proposed system.


Analysis and Design of SQR-Based High-Voltage LLC Resonant DC–DC Converter

Abstract:
This paper presents the analysis and design of an isolated high-voltage LLC resonant dc-dc full-bridge converter based on symmetrical quadrupler rectifier (SQR). Unlike conventional Cockcroft-Walton and full-bridge diode rectifiers, the SQR circuit provides significant improvement in power density by reducing the transformer turns-ratio without much increase in the output impedance. Moreover, the LLC converter can provide additional voltage boost, if operated, below the series resonant frequency of the LLC tank. The operating region of the converter is chosen in such a way that the converter always operates in ZVS for all line and load conditions with additional voltage boost. A new method based on basic differential equation is proposed for the accurate analysis and design of the converter and subsequently, the key results are compared with a first harmonic approximation based analysis method. A 120 V dc input, 2 kV output, 200 W laboratory prototype has been designed, built, and tested. Simulation and experimental results shown in this paper demonstrate the validity of the analysis and design of the presented converter.


Single-Switch Quasi-Resonant DC–DC Converter for a Pulsed Plasma Thruster of Satellites

Abstract:
Due to its low mass and medium impulse bit, the pulsed plasma thruster (PPT) is a suitable electric propulsion system for orbit maintenance and attitude control for nanosatellites. The PPT uses an igniter circuit to produce an arc in vacuum for plasma generation. In this paper, a new quasi-resonant converter topology is proposed for the PPT igniter. It consists of a resonant tank, a step-up transformer, and a Cockcroft-Walton voltage multiplier circuit. While other resonant converters require a switch bridge, the proposed approach uses only a single switch. This prevents the possible short-circuit of the same leg in a switch bridge caused by the noise interference or single event effect in space. Moreover, the switching control is realized without a dead time which simplifies the implementation. Both simulation and experimental results have validated that the proposed topology operates in a quasi-resonant state to realize zero-current switching. It reduces the switching noise, voltage spike, and switch’s conduction loss. Moreover, the proposed topology also has a better boost capability than some of the existing resonant converters.


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