Study of a DC voltage equalizing circuit and a zero‐sequence voltage control method for a diode‐clamped linear amplifier

2,3 This paper proposes a DC voltage equalizing circuit for a diode‐clamped linear amplifier (DCLA). The DCLA consists of series‐connected complementary MOSFETs and diode clamping circuits, with an experimental efficiency as high as 90% without switching operation. The DCLA requires a DC voltage equalizing circuit to divide the DC voltage into several levels. The proposed DC voltage equalizing circuit allows the use of a diode rectifier with a smoothing capacitor as a power supply for the DCLA. Zero‐sequence voltage control is proposed to improve the efficiency of the DCLA. As a result, a prototype 12‐series DCLA demonstrates an experimental efficiency as high as 94.7%. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 55–63, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21131     

Double‐Switch Series‐Resonant Cell‐Voltage Equalizer Using a Voltage Multiplier for Series‐Connected Energy Storage Cells

Series connections of energy storage cells, such as lithium‐ion cells and electric double‐layer capacitors (EDLCs), require cell‐voltage equalizers to ensure years of operation. Conventional equalizers require multiple switches, magnetic components, and/or secondary windings of a multiwinding transformer in proportion to the number of series connections, which usually makes them complex, expensive, bulky, and less extendable with increasing series connections. A double‐switch series‐resonant equalizer using a voltage multiplier is proposed in this paper. The double‐switch operation without a multiwinding transformer achieves simplified circuitry and good modularity at reduced size and cost, compared to conventional equalizers. Operational analyses were separately performed for the following two functional parts of the proposed equalizer: a series‐resonant inverter and a voltage multiplier. The mathematical analyses derived a dc‐equivalent circuit of the proposed equalizer, with which simulation analyses of even an hour's duration can be completed in an instant. Simulation analyses were separately performed for both the original and equivalent circuits. The simulation results of the derived circuit correlated well with those of the original circuit, thus verifying the derived dc‐equivalent circuit. A 5‐W prototype of the proposed equalizer was built for eight cells connected in series and an experimental equalization was performed for series‐connected EDLCs from an initially voltage‐imbalanced condition. The voltage imbalance was gradually eliminated over time, and the standard deviation in the cell voltages decreased to approximately 5 mV at the end of the experiment, thus demonstrating the equalization performance of the proposed equalizer.     

Electric double‐layer capacitor module with series‐parallel reconfigurable cell voltage equalizers

When electric double‐layer capacitors (EDLCs) are connected in series, a cell voltage imbalance occurs due to nonuniform cell properties. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energy of cells. In this study, we propose a series‐parallel reconfigurable cell voltage equalizer that is considered suitable for energy storage systems using EDLCs instead of traditional secondary batteries as the main energy storage sources. The proposed equalizer requires only EDLCs and switches as its main circuit elements, and it utilizes EDLCs not only for energy storage but also for equalization. An equivalent circuit model using equivalent resistors that can be regarded as an index of equalization speed is developed. Current distribution and cell voltage imbalancing during operation are quantitatively generalized. Experimental charge–discharge tests were performed on the EDLC modules to demonstrate the performance of the cell voltage equalizer. All the cells in the modules could be charged/discharged uniformly even when a degradation‐mimicking cell was intentionally included in the module. The resultant cell voltage imbalances and current distributions were in good agreement with those predicted by mathematical analyses. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(4): 38–50, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21287     

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     

Voltage balancing control of chain link converter application to interconnection system

An application of the chain link converter (CLC) system, which consists of multiple single‐phase voltage source converters (VSCs) connected in parallel or series, is studied as interconnection systems. In a CLC‐high voltage direct current transmission (HVDC) system, single‐phase converters must be connected in series on the DC side to make the DC voltage high, and the DC voltage of each converter must be controlled to the same value to get an appropriate capacity. This paper describes a DC voltage balancing control (DVBC) method between series converters. Simulations and simulator tests in steady states and in transient states were carried out to confirm behaviors of the CLC‐HVDC system. Those results confirmed the viability of CLC applications to interconnection systems. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Novel bifunctional converter‐based supercapacitor energy storage module with active voltage equalizing technology

A bifunctional converter module for supercapacitor energy storage based on an input‐series‐output‐series (ISOS) circuit is proposed in this paper. Compared to the existing topologies, the proposed circuit acts both as a supercapacitor cell voltage equalizer and as an output voltage regulator. During the charging process, series‐ connected flyback converters transfer energy from fully charged cells to the string via a bypass. Therefore, the fully charged cells maintain the rated terminal voltage, and the charging speed of the rest of the cells increases. During the discharging process, the output voltage of the module can be regulated with the same set of converters. The working principles during the discharging/charging processes are analyzed. The designs of the flyback converter and the control system are presented. A prototype consisting of three submodules is implemented. Experimental results verify the effectiveness of the proposed topology. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An Equalization Time Reduction Method Using a Pseudo‐Random Number Sequence for a Cell Voltage Equalization Circuit with an LC Series Circuit

When the cells of energy storage devices such as electric double‐layer capacitors are connected in series, it results in voltage imbalance in each cell because of the nonuniform properties of the individual cells. In a previous research, the authors proposed a novel cell voltage equalization circuit using an LC series circuit, and they examined the effectiveness of this circuit. However, the characteristics of the cell voltage equalization operation depend on each cell voltage difference. Therefore, the proposed circuit has a disadvantage that the equalization time tends to be longer than other cell voltage equalization circuits with a boosting circuit. This paper proposes an equalization time reduction method that uses a pseudo‐random number sequence generated by the linear congruential generators. The proposed method can reduce the average equalization time without adding any other active or passive elements. The effectiveness of the proposed method is verified through the experimental results. According to the experimental results, the proposed equalization time reduction method reduces the equalization time to 86.5% of the conventional method.     

Design and implementation of a high‐efficiency bidirectional DC‐DC Converter for DC micro‐grid system applications

This paper studies the design and implementation of a non‐isolated dual‐half‐bridge bidirectional DC‐DC converter for DC micro‐grid system applications. High efficiency can be achieved under wide‐range load variations by the zero‐voltage‐switching features and an adaptive phase‐shift control method. A three‐stage charging scheme is designed to meet the fast‐charging demand and prolong the lifetime of LiFePO₄ batteries. A digital‐signal‐processing control IC is used to realize the power flow control, DC‐bus voltage regulation, and battery charging/ discharging of the studied bidirectional DC‐DC converter. Finally, a 10 kW prototype converter with Enhanced Controller Area Network communication function is built and tested for micro‐grid system applications. A light‐load efficiency over 96% and a rated‐load efficiency over 98% can be achieved. Copyright © 2013 John Wiley & Sons, Ltd.     

A soft‐switching high step‐up DC‐DC converter with a single magnetic component

A soft‐switching high step‐up DC‐DC converter with a single magnetic component is presented in this paper. The proposed converter can provide high voltage gain with a relatively low turn ratio of a transformer. Voltage doubler structure is selected for the output stage. Due to this structure, the voltage gain can be increased, and the voltage stresses of output diodes are clamped as the output voltage. Moreover, the output diode currents are controlled by a leakage inductance of a transformer, and the reverse‐recovery loss of the output diodes is significantly reduced. Two power switches in the proposed converter can operate with soft‐switching due to the reflected secondary current. The voltages across the power switches are confined to the clamping capacitor voltage. Steady‐state analysis, simulation, and experimental results for the proposed converter are presented to validate the feasibility and the performance of the proposed converter. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental verification of a dynamic voltage restorer capable of significantly reducing energy‐storage element requirements

This paper deals with a dynamic voltage restorer (DVR) characterized by installing the shunt converter at the load side. The DVR can compensate for the load voltage when a voltage sag appears in the supply voltage. An existing DVR requires a large capacitor bank or other energy‐storage elements such as double‐layer capacitors or batteries. The DVR presented in this paper requires only a small DC capacitor intended for smoothing the DC‐link voltage. Moreover, three control methods for the series converter are compared and discussed to reduce the series‐converter rating, paying attention to the zero‐sequence voltages included in the supply voltage and the compensating voltage. Experimental results obtained from a 200‐V, 5‐kW laboratory system are shown to verify the viability of the system configuration and the control methods. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 73–82, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20460     

柔性直流输电系统MMC换流阀闭环充电策略

随着柔性直流输电系统的快速发展与广泛应用,其启动工况愈发具有多样性,MMC换流阀传统开环充电策略需要综合考虑系统状态变量进行参数配置,且配置难度大。由此提出了通用性的换流阀闭环充电控制策略,无需检测系统状态即能将子模块稳态电压控制在额定值,具有较好的适应性。首先,分析了柔性直流输电系统的三类充电回路及主动均压充电策略。其次,基于子模块特性不一致的均压需求分析,提出了完整的通用性闭环充电策略及对应的柔性直流输电系统的协调启动策略。最后通过PSCAD/EMTDC搭建了三端直流电网模型,仿真验证了闭环充电策略。结果表明闭合充电策略通用于各类换流站的启动充电过程,且可将子模块电压平稳充电至额定值,同时不存在桥臂过流及子模块过压等现象。     

一种延长电动汽车蓄电池寿命的均衡充电控制策略

电动汽车用动力电池组都是由多个单体电池串联而成,由于单体电池的性能不可能完全一致,串联使用过程中,初期的细微差异在每次充放电的放大作用下,一段时间后单体电池间的性能差异就会逐渐增大,从而导致电池组性能急剧下降和循环寿命缩短。通过分析电池组提前失效的原因,针对耗散型均衡控制电路,深入研究电池组均衡充电控制的电路模型,并在此基础上提出一种既能够实现电池组快速充电,又能够消除单体电池不一致对电池组循环寿命影响的均衡充电控制策略。根据所提出的均衡充电控制策略,对72 V/120 AH铅酸蓄电池组进行对比测试,实验结果说明了该策略的有效性。     

Control methods and compensation characteristics of a series active filter for neutral conductor

With an increase in the number of electronic devices, such as personal computers, connected to power distribution lines in commercial buildings, problems associated with their use, such as voltage distortion on utility outlets and excessive neutral current on the distribution lines, become more and more serious. This paper shows control methods and compensation characteristics of series active filters connected to the neutral conductor. The distinctive functions of the proposed active filter are the mitigation of third harmonic voltage and the reduction of neutral current in three‐phase four‐wire distribution systems. The required kVA rating of the proposed active filter is less than 10% of that of the harmonic producing leads. A control method of the DC capacitor voltage on the active filter circuit is also described. It was experimentally demonstrated that one of these two functions of the active filter (to mitigate harmonics or to reduce the neutral current) can be realized selectively and that the DC capacitor voltage of the active filter can be regulated to a desired value. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 53–63, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20227     

Comprehensive comparison of FACTS devices for exclusive loadability enhancement

A complete comparison of a number of well‐known flexible alternating current transmission system (FACTS) devices for static voltage stability enhancement is presented. Various performance measures including power–voltage (P–V) curves, voltage profiles, and power losses are compared under normal and contingency conditions. The importance of proper modeling of FACTS devices, including the DC side, is emphasized because, at their limits, most of these devices behave like a fixed capacitor or inductor. A simple placement technique of series FACTS devices and unified power flow controller (UPFC) is proposed considering exclusive loading margin enhancement. A new idea of loading margin increase per cost is proposed to find the appropriate FACTS devices for investment. The paper provides a guide for utilities to have an appropriate choice of FACTS device for enhancing static voltage stability and loading margin by comparing technical merits and demerits of each of these devices in terms of system performance. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

无通信互联线储能系统的直流母线协调控制策略

针对无通信互联线的储能系统如何在不增加系统成本和复杂度的前提下维持直流母线功率平衡及电压稳定,提出了一种直流母线协调控制策略,DC/AC变流器采用定直流电压或定交流电压控制,两台DC/DC变换器采用包含电池充放电控制的改进型二阶直流电压偏差控制。通过对系统典型工况的分析,说明了系统中各个装置是如何协调工作的。搭建了微网实验平台对所提出的控制策略进行了实验验证,实验结果证明了该控制策略的有效性和实用性。     

Zero‐voltage switching modular equalization system for series super‐capacitor string

This paper presents a zero‐voltage‐switching modular equalization for series super‐capacitor string in a large energy storage system. The zero‐voltage working scheme is analyzed based on Power Simulation (PSIM) to verify its validity. An equalization system test for 16‐super‐capacitor cells is conducted under voltage‐imbalanced conditions. The power flow model, switching patterns, and zero‐voltage gap are discussed. The simulation and experimental results are presented, indicating that the equalization not only inherits the advantages of traditional inductor‐based super‐capacitor equalization system, but also brings some merits, such as flexible, low switching loss, and highly modularized.     

Series resonant high‐voltage DC–DC converter with reduced component count

This paper proposes a novel zero‐current‐switching series resonant high‐voltage DC–DC converter with reduced component count. The series resonant inverter in the proposed topology has two power switches (insulated‐gate bipolar transistors, IGBTs), two resonant capacitors, and only one high‐voltage transformer (HVT) with center‐tapped primary windings. The power switches are connected in the form of a half‐bridge network. The leakage inductances of the transformer's primary windings together with the resonant capacitors form two series resonant circuits. The series resonant circuits are fed alternately by operating the power switches with interleaved half switching cycle. The secondary winding of the HVT is connected to a bridge rectifier circuit to rectify the secondary voltage. The converter operates in the discontinuous conduction mode (DCM) and its output voltage is regulated by pulse frequency modulation. Therefore, all the power switches turn on and off at the zero‐current switching condition. The main features of the proposed converter are its lower core loss, lower cost, and smaller size compared to previously proposed double series resonant high voltage DC–DC converters. The experimental results of a 130‐W prototype of the proposed converter are presented. The results confirm the excellent operation and performance of the converter. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Series-type charger with output voltage automatically regulated and hot swap

Since the traditional series-type charger has no function of hot swap, a new series-type charger with hot swap is presented herein. In this study, hot-swap battery and stopping charging battery are achieved by floating voltage detection and battery bypass detection. Furthermore, by means of controlling the voltage across the collector of the bipolar junction transistor (BJT) and the ground, the output voltage of the DC–DC converter can be automatically adjusted. Accordingly, the BJT can always work under the active region with a designed constant voltage across it for any number of batteries in the steady state, reducing undesired conduction loss. Also, one constant current control circuit is utilized, which is connected in series with the voltage and bypass detectors. Above all, unlike the traditional series-type charger with the active equalizer, there is no energy transferred among batteries in the proposed charger. Finally, the proposed series-type charger with four battery channels is designed and applied to charging 18650 Li-ion batteries. Via some experimental results, the effectiveness of the proposed charger can be verified.     

太阳能LED照明系统的设计

介绍了一种基于铅酸蓄电池均充模式的太阳能LED照明系统。太阳能电池的输出电压由DC/DC转换模块进行稳压;控制器对蓄电池进行荷电状态(SOC)检测和充电方式选择,并具有过放电、过充电保护;采用LED照明,发光效率高、功耗低。     

A constant DC voltage control‐based strategy for an active power quality compensator in electrified railways with improved response

This paper proposes a constant DC voltage control‐based strategy for an active power quality compensator (APQC) used in electrified railways. The proposed strategy consists of only an I‐PD‐based constant DC capacitor voltage control with an added moving‐average type low‐pass filter (LPF). The added LPF improves the response of the constant DC capacitor voltage control for the APQC. Thus we offer the simplest control method for the APQC used in electrified railways with improved response. The basic principle of the proposed control strategy is discussed in detail, and then confirmed by digital computer simulation using the PSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that balanced source currents with unity power factor are obtained on the primary side of the Scott transformer in the traction substation systems, improving the response by one‐fourth as compared to that of the previously proposed control method. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.