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that turn on or turn off in less than a microsecond. Power flow is controlled accurately, efficiently, and quickly by the converter due to the fast action of power semiconductor devices. However, the voltage and current of a device have an overlapping time during turn‐on or turn‐off transients, which results in switching loss, higher stress on the devices, and Electromagnetic Interference (EMI) noise. The switching loss of a converter is proportional to its operating switching frequency. Accordingly, switching frequency is restricted in order to achieve expected conversion efficiency. The lower switching frequency may result in bulky passive components, lower dynamics, higher audible noise, etc. Aiming to reduce or eliminate the voltage and current overlapping during the switching actions, soft‐switching technology occurs. It is a way to shape the voltage and current of the power device during switching transients so that the overlapping of voltage and current on the power device during switching commutations is reduced. It not only reduces switching loss and EMI noise but also suppresses stress on the power devices. Soft‐switching has been widely utilized in DC–DC converters in switching power supply and single‐phase inverters for induction heating. However, there is almost no book to systematically investigate soft‐switching technology of three‐phase converters or inverters. As we know, applications of soft switching to three‐phase converters/inverters have a large potential in the future in distributed power generation, data centers, industrial power supplies, Electric Vehicle (EV) charging stations, high‐speed motor drives, etc. This book tries to give readers an overview of the progress of the soft‐switching three‐phase conversion.

This book emphasizes circuit analysis, pulse‐width‐modulation (PWM) control, and the design of zero‐voltage‐switching (ZVS) three‐phase converters. First, this book gives an introduction to the fundamentals of soft‐switching three‐phase conversion. Requirements for three‐phase power conversions such as conversion efficiency, power density, and impact of soft‐switching technique are explained. It includes an overview of the progress of soft‐switching technology for three‐phase converters. It introduces applications of soft‐switching three‐phase power conversion to renewable energy generation, industry, transportation, etc. A ZVS space vector modulation (ZVS‐SVM) is introduced, which is modified from SVM to adapt to the soft‐switching operation of the three‐phase converters. A generic soft‐switching modulation method for three‐phase converters, edge‐aligned PWM (EA‐PWM) is introduced. Then circuit analysis, soft‐switching condition, and control of active‐clamped three‐phase converter with EA‐PWM are provided. Second, the book will introduce applying soft‐switching technology to three‐phase rectifiers. Two types of soft‐switching circuits are investigated. It includes circuit analysis, soft‐switching condition derivation, circuit parameters design, and experiment results of the three‐phase rectifier prototypes. Afterward, applying soft‐switching technology to three‐phase grid inverters are studied. Two types of soft‐switching circuits are introduced. Similarly, it includes circuit analysis, soft‐switching condition derivation, circuit parameters design, and experiment results of the three‐phase inverter prototypes. Since resonant inductor is a critical component with respect to magnetic and copper loss, thermal characteristics, and size, the design of the resonant inductor is explained. In addition, the optimization of a grid inverter is investigated with regard to power density and efficiency. Finally, due to the increasing application of the wide‐bandgap device to three‐phase converters, this book investigates the impact of SiC devices on soft‐switching three‐phase converters with respect to efficiency and power density enhancement. Three examples of soft‐switching converters with SiC devices are studied, which include soft‐switching SiC three‐phase grid inverter, soft‐switching SiC single‐phase grid inverter with active power decoupling, and soft‐switching SiC three‐phase back‐to‐back (BTB) converter. They are helpful for the readers to understand how the practical system works and can be a guide to build a test bench in a laboratory. This book may be helpful for readers who hope to have knowledge of circuit analysis, PWM control and design of ZVS three‐phase converters, and deep understanding of the soft‐swithcing technique of three‐phase conversions. It is suitable for both undergraduate and graduate levels and may serve as a useful reference for academic researchers, engineers, managers, and other professionals in the industry. Most of the chapters include descriptions of fundamental and advanced concepts, supported by many illustrations.

      Dr. Dehong Xu has designed the contents and writing plan of the book. He wrote Chapters 1, 2, and 3. Dr. Rui Li wrote Chapters 4, 5, and 6. Dr. Ning He wrote Chapters 7, 8, and 10. Mr. Jinyi Deng wrote Chapters 9 and 12. Mr. Yuying Wu wrote Chapter 11. Dr. Dehong Xu has helped revise all the chapters of the book.

      The authors would like to acknowledge the contribution of colleagues and former graduate students of Zhejiang University, Dr. Gang Chen, Dr. Bo Feng, Dr. Chengrui Du, Dr. Keyan Shi, Dr. Yenan Chen, Dr. Min Chen, Dr. Changsheng Hu, Dr. Ke Ma, Mr. Zhiyuan Ma, Mr. Yingfeng Zhu, Ms. Yawen Li, Mr. An Zhao, Mr. Zhengyu Ye, and Mr. Ruizhe Wang, for developing the soft‐switching technology for the three‐phase converters. We acknowledge the tireless efforts and assistance of Wiley Press editorial staff.

      Dehong Xu

      Rui Li

      Ning He

      Jinyi Deng

      Yuying Wu

      Nomenclature

      Subscripts

      aphase Abphase Bcphase Cggate of switchmmodulationrresonancesswitching cycle

      Superscripts

      

reference vectorxrefreference value

      Variables

vvariable voltageVconstant voltage

voltage vectorivariable currentIconstant current

current vectorvdcinstantaneous voltage of DC sideVdcDC component of voltageidcinstantaneous current of DC sideIdcDC component of currentTsswitching periodTrresonant periodfsswitching frequencyfrresonant frequencyflgrid frequencyωrresonant angular frequencyωlgrid angular frequencyφinitial phase angle of gridPactive powerQreactive powerpinstant powerPFpower factorηefficiencydduty cycleϕmagnetic fluxψmagnetic flux linkage

Part 1 Fundamental of Soft‐switching

1 Introduction

      In this chapter, an overview of soft‐switching technology for three‐phase power electronics converters and its evolution are briefly introduced, and the challenges and trends in the soft‐switching three‐phase converters are discussed.

1.1 Requirement

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