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Published in IET Power Electronics Received on 30th September 2013 Revised on 17th December 2013 Accepted on 18th January 2014 doi: 10.1049/iet-pel.2013.0751

ISSN 1755-4535

Three-phase interleaved high-step-up converter with coupled-inductor-based voltage quadrupler
Yihua Hu, Weidong Xiao, Wuhua Li, Xiangning He
College of Electrical Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China E-mail: woohualee@zju.edu.cn

Abstract: This paper proposes a high-efficient DC–DC solution with the features of galvanic isolation, high-voltage gain, zero voltage switching operation, low input current ripple and high-power density. The converter is implemented by a three-phase coupled inductor bridge to remove the bulky input electrolytic capacitors. The introduced active clamp circuit recycles the energy stored in the leakage inductance and absorbs the voltage spikes on the main switch voltage. The series configuration with a voltage doubler at the second side contributes to a high-voltage gain and reduces the voltage stress across the rectifier devices. The output diode reverse-recovery problem is naturally mitigated by the leakage inductance of the coupled inductors. Moreover, the active control with a neutral-point potential balance and a phase-deficient operation of the proposed converter are also studied. A converter prototype is designed and evaluated to verify the theoretical analysis and demonstrate a superior performance over the prior studies.

1

Introduction

Distributed generation requires high-step-up DC–DC converters to accommodate the low-voltage nature of batteries, fuel cells and photovoltaic cells [1, 2]. For the non-isolated applications, various topologies have been proposed for a high-step-up voltage operation by using a coupled inductor or a switched capacitor, which are reported and summarised in [3–15]. When the feature of galvanic isolation is required for the high-voltage gain converters, the research objective mainly focuses on the high efficiency, the low input current ripple and the low-voltage stress of the devices. The high-voltage conversion gain is traditionally achieved by applying the high-turn-ratio of the transformer and utilising the conventional full bridge converters [16]. However, the leakage of the coupled inductance energy causes high-voltage spikes, which cause potential damage to the switching devices [17]. In general, the high-turn-ratio transformer is not as efficient as its low-turn-ratio counterpart since the significant length of the secondary windings introduces a proximity effect and an additional copper loss. To suppress the surge voltage, the application of passive clamp circuits generally deteriorates the system efficiency [17]. Furthermore, the full bridge topology faces the risk of a shoot-through phenomena across the bridge arm. Therefore the research direction should focus on the converter topologies that can achieve a high-step-up conversion ratio, maintain a reasonable duty ratio and avoid high-turn-ratios in the transformer design. A voltage lift circuit in the second side was developed in [17] to achieve a high-voltage gain. The doubler circuit utilises two capacitors, which are charged in parallel and
IET Power Electron., 2014, Vol. 7, Iss. 7, pp. 1841–1849 doi: 10.1049/iet-pel.2013.0751

discharged in series. The Flyback topology has been improved by the implementation of the active clamp [18, 19] and the voltage multiplier [18] to recycle the leakage energy and reduce the transformer turn ratio. The voltage multiplier is achieved by the switching capacitors at the secondary side. However, since the coupled inductor shall handle all the transferring energy in the Flyback converters, the proposed solution [17–19] faces the constraint of converter power capacity. One interleaved solution has been proposed in [20] to improve the power capacity and the conversion efficiency. It also includes the windingcross-coupled inductors to achieve the functions of a high conversion ratio, soft switching and active clamping, which are useful features for both the isolated buck and boost converters. A hybrid of the Flyback-forward converter using a full bridge was investigated in [21, 22], which demonstrated the advantage of zero voltage switching (ZVS). The proposed topology includes the active clamping circuit and the coupled inductor bridge (CIB), which recycle the leakage energy and double the voltage output, respectively. A high-step-up current-fed multi-resonant converter is proposed in [23, 24], which is composed of a current source generator, a resonant tank and an output voltage doubler, respectively. However, the power capacity of the above topologies is limited by the transformer design. In [25], an auxiliary step-up circuit is proposed to be integrated with the isolated Cuk-derived voltage source inverter to achieve a high conversion ratio and prevent extreme duty ratios. The concept of an isolating intercell transformer has been implemented in [26] to support the features of a high-step-up but low transformer turn ratio. However, the bridge structure indicates the disadvantages of
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www.ietdl.org a shootthrough risk and a high-voltage stress across the switching devices, especially in a high voltage side. One topology, namely, a two transformer current fed converter, is proposed in [27] for the high-voltage applications which achieve a low inrush current, a high conversion ratio and a low duty cycle value (