A matching transformer‐less inrush current suppressor for transformers using a series‐connected small‐rated voltage‐source PWM converter—consideration of the control gains and required ratings of the PWM converter

This paper proposes a new inrush current suppressor using a series‐connected small‐rated PWM converter for a transformer. The PWM converter is directly connected in series between the source and transformer without a matching transformer. The inrush phenomena of the matching transformer, thus, can be avoided. The control gain and required ratings of the series‐connected small‐rated PWM converter are discussed in detail. The capacity of the DC capacitor of the PWM converter is also discussed considering the active power flows into the PWM converter. The PSCAD/EMTDC is used to verify the validity of the proposed inrush current suppressor. A prototype experimental model is constructed and tested. The experimental results demonstrate that the proposed suppressor can perfectly overcome the inrush phenomena of transformers. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 45–55, 2007; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/eej.20374     

Compensation for magnetizing inrush currents in transformers using a PWM inverter

When a transformer is connected to a circuit, under certain conditions, magnetizing inrush currents may be about ten times the full load current of the transformer. The currents contain a large amount of harmonic components and cause some relays to trip out. In this paper, the magnetizing inrush currents are compensated using a PWM inverter. The magnetizing inrush currents are detected and the PWM inverter generates compensating currents for the inrush currents. Hysteresis current controllers are used for fast response. The validity of this compensation is investigated by the simulation results. In addition, hardware implementation for the compensator is accomplished to verify the simulation results. Moreover, for the compensator, the relation between the compensating characteristics, the maximum switching frequency, and the coupling reactor is discussed based on the simulation results. Finally, characteristics of two current controllers (hysteresis band current controller and ramp‐comparison controller) are compared and it is shown that the hysteresis band current controller is more suitable for the compensator. The PSCAD/EMTDC electromagnetic transient simulator is used for the simulations. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(2): 53–64, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10023     

Control of fault current limiter by series‐connected voltage sag compensator

This paper describes a control scheme of fault current limiter by series voltage injection. The current limiter proposed in this study is based on the use of a SMES‐based series‐connected voltage sag compensator, which has been previously studied by the authors, for controlling fault current caused by short circuit on the load side. An algorithm for fast discriminating between power system voltage sag and load‐side short circuit is proposed for the equipment to correctly function either for voltage sag compensation or for fault current limiting purpose. Furthermore, a new control strategy based on output voltage phase control of the series compensator is proposed for current limiting with good waveform characteristics and low active power absorption. Experimental results demonstrated the validity of the proposed strategy. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 64–72, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20128     

LLC resonant DC–DC converter with series‐connected primary windings of transformer

This paper proposes a zero‐voltage switching (ZVS) LLC resonant step up DC–DC converter with series‐connected primary windings of the transformer. The series resonant inverter in the proposed topology has two power switches (MOSFETs), two resonant capacitors, two resonant inductors, and only one transformer with center‐tapped primary windings. The power switches are connected in the form of a half‐bridge network. Resonant capacitors and inductors along with the primary windings of the transformer form two series resonant circuits. The series resonant circuits are fed alternately by operating the power switches with an interleaved half switching cycle. The secondary winding of transformer is connected to a bridge rectifier circuit to rectify the output voltage. The converter operates within a narrow frequency range below the resonance frequency to achieve ZVS, and its output power is regulated by pulse frequency modulation. The converter has lower conduction and switching losses and therefore higher efficiency. The experimental results of a 500‐W prototype of proposed converter are presented. The results confirm the good operation and performance of the converter. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Implementation of parallel zero‐voltage switching converter with series‐connected transformers

This paper presents a parallel zero‐voltage switching (ZVS) DC–DC converter with series‐connected transformers. In order to increase output power, two transformers connected in series are used in the proposed converter. Two buck‐type converters connected in parallel have the same switching devices. The primary windings of series‐connected transformers can achieve the balanced secondary winding currents. The current doubler rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding. Thus, the current ripple on the output capacitor is reduced, and the size of the output choke and output capacitor are reduced. Only two switches are used in the proposed circuit instead of four switches in the conventional parallel ZVS converter to achieve ZVS and output current sharing. Therefore, the proposed converter has less power switches. The ZVS turn‐on is implemented during the commutation stage of two complementary switches such that the switching losses and thermal stresses on the semiconductors are reduced. Experimental results for a 528‐W (48 V/11 A) prototype are presented to prove the theoretical analysis and circuit performance. Copyright © 2011 John Wiley & Sons, Ltd.     

A novel multi‐output high‐voltage‐isolated power supply system for semiconductor device series‐connected switches

This paper presents a novel scheme of a multi‐output power supply for solid‐state switches based on series‐connected semiconductor devices. By using the loosely transforming method, the system can realize high‐voltage isolation and a compact size, and its application range can be easily expanded to modular designed switch stacks for higher power ratings. The circuit structure and working principles are described. Based on the system operating equations, the design methodology is proposed and applied for parameter specification of a power supply system of two series‐connected switch stacks containing 20 outputs. Detailed calculations are given, and experimental results prove the feasibility of the proposed scheme. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A three‐phase constant‐current source using an immittance converter

The term immittance converter refers to an impedance–admittance converter. The immittance converter has an input impedance that is proportional to the admittance of the load connected across output terminals. In this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, it converts a constant‐voltage source into a constant‐current source and a constant‐current source into a constant‐voltage source. It is well known that the quarter wavelength transmission line shows immittance conversion characteristics. However, it has a very long line length for the switching frequency, and is not suitable for power electronics applications. We thus proposed immittance converters that consist of lumped elements L, C and show improved immittance conversion characteristics at a resonant frequency. A three‐phase constant‐current source is proposed in this paper. It is possible to realize this by a simple circuit using an immittance converter. In this paper, circuit operation, characteristic equations, and results of simulation are described. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 47–54, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20078     

A study of PWM carrier settings and harmonic reduction of a multiply connected voltage source type AC/DC converter

This paper discusses the voltage harmonics generated from the multiple connected voltage source type self‐commutated converter, which is switched with PWM (Pulse Width Modulation) signal generated by comparing sinusoidal signal wave with triangle carrier wave. The conventional harmonics analysis of the multiple connected converters directly calculates Fourier coefficients to the output waveform. This paper formularized the harmonics component of single converter in a convenient expression for the analysis of multiple connected converters using the multiple Fourier transform. The obtained equations not only can give harmonics of the multiple connected converters easily, but also can give index to determine the suitable settings of the PWM carrier for harmonics reduction. The theoretical design of the harmonics reduction of the converter output is confirmed through EMTP simulations. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 16–25, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10184     

A three‐phase voltage‐source PWM inverter system characterized by sinusoidal output voltage with neither common‐mode voltage nor normal‐mode voltage

This paper deals with an inverter system integrating a small‐rated passive EMI filter with a three‐phase voltage‐source PWM inverter. The purpose of the EMI filter is to eliminate both common‐mode and normal‐mode voltages from the output voltage of the inverter. The motivation of this research is based on the well‐known fact that the higher the carrier or switching frequency, the smaller and the more effective the EMI filter. An experimental system consisting of a 5‐kVA inverter, a 3.7‐kW induction motor, and a specially designed passive EMI filter was constructed to verify the viability and effectiveness of the EMI filter. As a result, it is shown experimentally that both three‐phase line‐to‐line and line‐to‐neutral output voltages look purely sinusoidal as if the inverter system were an ideal variable‐voltage, variable‐frequency power supply when viewed from the motor terminals. This results in complete solution of serious issues related to common‐mode and normal‐mode voltages produced by the inverter. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(4): 88–96, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10206     

A novel quasi‐Z‐source indirect matrix converter

A new type of three‐phase quasi‐Z‐source indirect matrix converter (QZS‐IMC) is proposed in this paper. It uses a unique impedance network for achieving voltage‐boost capability and making the input current in continuous conduction mode (CCM) to eliminate the input filter. The complete modulation strategy is proposed to operate the QZS‐IMC. Meanwhile, a closed‐loop DC‐link peak voltage control strategy is proposed, and the DC‐link peak voltage is estimated by measuring both the input and capacitor voltages. With this proposed technique, a high‐performance output voltage control can be achieved with an excellent transient performance even if there are input voltage and load current variations. The controller is designed by using the small‐signal model. Vector control scheme of the induction motor is combined with the QZS‐IMC to achieve the motor drive. A QZS‐IMC prototype is built in laboratory, and experimental results verify the operating principle and theoretical analysis of the proposed converter. The simulation tests of QZS‐IMC based inductor motor drive are carried out to validate the proposed converter's application in motor drive. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel robust current control approach using adaptive line enhancer for three‐phase current‐source active power filter

An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014     

High‐order harmonic resonance phenomena of a voltage‐sourced converter in cable system

This paper presents high‐order harmonic resonance phenomena of voltage‐sourced converters (VSC). When a voltage‐sourced converter is connected to a power system with cables, there is a possibility that minute high‐order harmonic voltages of a voltage‐sourced converter are magnified by a series resonance and a parallel resonance, and high‐order harmonic resonance phenomena are determined by this study. The cause of high‐order harmonic resonance phenomena is investigated and elucidated by the analysis using EMTP. In addition, it is verified that high‐order harmonic resonance phenomena occur as a practical matter. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 26–35, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20054     

Improved control‐to‐output characteristics of a PWM buck‐boost converter

An indirect control variable for improving the control‐to‐output characteristics of a Pulse Width Modulation (PWM) buck‐boost converter is introduced in this letter. The voltage gain and the small‐signal model of the buck‐boost converter are reviewed. The actual voltage command at one input of the PWM comparator is from the proposed indirect control variable and the peak value of the high‐frequency PWM carrier. The resulted voltage gain function appears proportional to this indirect control command. Also the dependence of the DC gain of the control‐to‐output transfer function on the duty cycle is eliminated. Experimental results conform well to the theoretical analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

A high‐efficiency isolated DC/DC converter using series connection on the secondary side

This paper proposes a new circuit topology for a high‐efficiency isolated DC/DC converter using series compensation. The proposed converter consists of a high‐efficiency resonance half‐bridge converter and a series converter. The series converter regulates the output voltage and provides only the differential voltage between the input voltage and output voltage. Therefore, the circuit achieves high efficiency when the input voltage is almost equal to the output voltage, because then only the resonance converter will operate. In this paper, the approach employed to achieve high efficiency by using the proposed series compensation method is introduced. In addition, the fundamental operation and the method of designing the proposed circuit are described. The suitability of the proposed circuit was confirmed by performing experiment and loss analysis, and the maximum efficiency achieved was 96.2%. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 42–52, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22330     

A step‐up PWM DC–DC converter for renewable energy applications

A step‐up pulse width modulation (PWM) direct current (DC)–DC converter is presented in this paper, which has its origin in quasi Z‐source inverter. Analysis of this converter in steady state is presented, and relevant expressions are derived for the proposed converter operating in continuous conduction mode. The power loss expressions for each component of the converter are derived, and thereby, obtained expressions for overall converter efficiency are presented. Further, a dynamic model is derived to design an appropriate controller for this converter. The simulation and experimental results are presented to support the theoretical analysis. The advantages such as continuous input current, high step‐up gain at lower duty ratio, and common ground for source, load, and switch makes the converter suitable for renewable energy applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Steady‐state solutions of a voltage source converter with dq‐frame controllers by means of the time‐domain method

A voltage source converter (VSC) is one of the most widely used power converters in a power system. In this paper, a time‐domain‐based accelerated steady‐state method is proposed to solve for a closed‐loop pulse‐width modulated (PWM) VSC with dq‐frame controllers, which is able to account for the harmonic interactions between the converter and the rest of the power network, between the AC and DC sides of a VSC, and between the converter and its controllers. The proposed time‐domain method is based on the modified time‐domain shooting method, where the Jacobian matrix is updated by the quasi‐Newtons method. This will drastically increase the computation efficiency as it avoids re‐evaluating and inverting the Jacobian matrix, whose size is usually very large for a PWM‐VSC due to high number of times of switching. All the results are shown to be consistent with those obtained by a PSCAD/EMTDC model, which has been validated with the experiment in a previous publication. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A novel three‐phase converter using a three‐phase series chopper

This paper proposes a novel three‐phase converter using a three‐phase series chopper. The proposed circuit is composed of three switching devices, three‐phase diode bridge, input reactors, and LC low‐pass filter. In the conventional circuit, which combines three‐phase diode bridge and boost voltage chopper, to obtain sinusoidal input current the output voltage must be two or three times larger than the maximum input line voltage. However, in the proposed circuit, the input current can be controlled to be sinusoidal also when the output voltage is the same as the maximum input line voltage. This can be achieved because in the proposed circuit the discharging current of the reactors does not flow through the voltage source. The control method of the proposed circuit is as simple as that of the conventional circuit since all three switching devices are simultaneously turned on and off. This paper discusses the theoretical analysis and the design of the proposed circuit. In addition, simulation and experimental results are reported. The proposed circuit has obtained a 93% efficiency, and 99.7% at 1.3kW load as the input power factor. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 79–88, 2000     

Analysis and implementation of a high‐efficiency zero‐voltage‐zero‐current‐switching DC–DC converter

A high‐efficiency zero‐voltage‐zero‐current‐switching DC–DC converter with ripple‐free input current is presented. In the presented converter, the ripple‐free boost cell provides ripple‐free input current and zero‐voltage switching of power switches. The resonant flyback cell provides zero‐voltage switching of power switches and zero‐current switching of the output diode. Also, it has a simple output stage. The proposed converter achieves high efficiency because of the reduction of the switching losses of the power switches and the output diode. Detailed analysis and design of the proposed converter are carried out. A prototype of the proposed converter is developed and its experimental results are presented for validation. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis and design of a half‐bridge LLC series resonant converter employing two transformers

This paper presents a two‐transformer LLC series resonant converter (SRC), which is derived from incorporating two identical converters. The proposed converter allows a low‐profile power supply design for liquid crystal display (LCD) TVs and servers. The presented converter can equally share the total load current between two transformers and the output rectifier modules. Therefore, the heat problem can be effectively relieved. The steady‐state analysis and design of this new two‐transformer LLC SRC are described. The experimental results are recorded for a prototype converter with an output voltage of 12thinspaceV, an output power of 300 W, and a resonant frequency of 74 kHz. Copyright © 2011 John Wiley & Sons, Ltd.