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CPSS Power Electronics Series Huafeng Xiao · Ruibin Wang · Chenhui Niu · Yun Liu · Kairong Qian High-Frequency Soft-Switching Transformerless Grid-Connected Inverters CPSS Power Electronics Series Series Editors Wei Chen, Fuzhou University, Fuzhou, Fujian, China Yongzheng Chen, Liaoning University of Technology, Jinzhou, Liaoning, China Xiangning He, Zhejiang University, Hangzhou, Zhejiang, China Yongdong Li, Tsinghua University, Beijing, China Jingjun Liu, Xi’an Jiaotong University, Xi’an, Shaanxi, China An Luo, Hunan University, Changsha, Hunan, China Xikui Ma, Xi’an Jiaotong University, Xi’an, Shaanxi, China Xinbo Ruan, Nanjing University of Aeronautics and Astronautics, Nanjing Shi, Jiangsu, China Kuang Shen, Zhejiang University, Hangzhou, Zhejiang, China Dianguo Xu, Harbin Institute of Technology, Haerbin Shi, Heilongjiang, China Jianping Xu, Xinan Jiaotong University, Chengdu, Sichuan, China Mark Dehong Xu, Zhejiang University, Hangzhou, Zhejiang, China Xiaoming Zha, Wuhan University, Wuhan, Hubei, China Bo Zhang, South China University of Technology, Guangzhou Shi, Guangdong, China Lei Zhang, China Power Supply Society, Tianjin, China Xin Zhang, Hefei University of Technology, Heifei Shi, Anhui, China Zhengming Zhao, Tsinghua University, Haidian Qu, Beijing, China Qionglin Zheng, Beijing Jiaotong University, Haidian, Beijing, China Luowei Zhou, Chongqing University, Chongqing, Sichuan, China This series comprises advanced textbooks, research monographs, professional books, and reference works covering different aspects of power electronics, such as Variable Frequency Power Supply, DC Power Supply, Magnetic Technology, New Energy Power Conversion, Electromagnetic Compatibility as well as Wireless Power Transfer Technology and Equipment. The series features leading Chinese scholars and researchers and publishes authored books as well as edited compilations. It aims to provide critical reviews of important subjects in the field, publish new discoveries and significant progress that has been made in development of applications and the advancement of principles, theories and designs, and report cutting-edge research and relevant technologies. The CPSS Power Electronics series has an editorial board with members from the China Power Supply Society and a consulting editor from Springer. Readership: Research scientists in universities, research institutions and the industry, graduate students, and senior undergraduates. · · · Huafeng Xiao Ruibin Wang Chenhui Niu · Yun Liu Kairong Qian High-Frequency Soft-Switching Transformerless Grid-Connected Inverters Huafeng Xiao Ruibin Wang College of Electrical Engineering College of Electrical Engineering Southeast University Southeast University Nanjing, Jiangsu, China Nanjing, Jiangsu, China Chenhui Niu Yun Liu China Huaneng Jiangsu Company College of Electrical Engineering Nanjing, Jiangsu, China Southeast University Nanjing, Jiangsu, China Kairong Qian China Huaneng Jiangsu Company Nanjing, Jiangsu, China ISSN 2520-8853 ISSN 2520-8861 (electronic) CPSS Power Electronics Series ISBN 978-981-19-3037-9 ISBN 978-981-19-3038-6 (eBook) https://doi.org/10.1007/978-981-19-3038-6 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 This work is subject to copyright. 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The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Contents 1 Introduction ................................................... 1 1.1 Development History of Soft-Switching Inverters ............... 1 1.2 Resonant DC-Link Inverters ................................. 3 1.2.1 Origin and Configuration of RDCLI .................... 3 1.2.2 Conventional RDCLI ................................. 3 1.2.3 Actively Clamped RDCLI ............................. 5 1.2.4 Parallel RDCLI ...................................... 6 1.3 Resonant Pole Inverters ..................................... 8 1.3.1 Origin and Configuration of RPI ....................... 8 1.3.2 Conventional RPI .................................... 8 1.3.3 Auxiliary Resonant Commutated Pole Inverter ........... 9 1.4 Freewheeling Resonance Tank Inverters ....................... 12 1.4.1 FRTI with Single-Quadrant Resonance Networks ......... 12 1.4.2 FRTI with Two-Quadrant Resonance Networks ........... 13 References ..................................................... 14 2 High-Frequency Transformerless Grid-Connected Inverters and Related Issues .............................................. 17 2.1 High-Frequency Operation Requirements for TLIs .............. 17 2.1.1 High Power Density and Low Volume ................... 18 2.1.2 Low Cost ........................................... 18 2.1.3 High Performance .................................... 19 2.2 Switching Loss Issue ........................................ 19 2.2.1 Origin of Switching Loss .............................. 19 2.2.2 Semiconductor Related Solutions ....................... 20 2.2.3 Circuit Related Solutions .............................. 21 2.3 EMI Issue ................................................. 21 2.4 Reactive Power Issue ....................................... 22 References ..................................................... 22 v vi Contents 3 Zero-Current-Transition TLIs with Switching-Loss-Free ........... 25 3.1 ZCT Trajectory and Implementing Cells with Self-compensation Mode ................................ 25 3.2 SLF-H6 Inverter ............................................ 28 3.2.1 Derivation of SLF-H6 Topology ........................ 28 3.2.2 Operation Principle ................................... 30 3.2.3 Conditions for Achieving SLF-H6 ...................... 34 3.2.4 Parameter Design of Resonant Components .............. 35 3.2.5 Experimental Verification ............................. 36 3.3 SLF-HERIC Inverter ........................................ 41 3.3.1 Derivation of SLF-HERIC Topology .................... 41 3.3.2 Operation Principle ................................... 42 3.3.3 Conditions for Achieving SLF-HERIC .................. 47 3.3.4 Experimental Verification ............................. 48 References ..................................................... 51 4 Zero-Current-Transition TLIs with Full Power Factor Range ...... 53 4.1 Two-Quadrant ZCT Resonance Network ....................... 53 4.1.1 Implementing Cells of ZCT Trajectory with Load-Related Radius ............................. 54 4.1.2 Derivation of TQ-ZCT-RN ............................ 55 4.2 SLF-HERIC-FPF Inverter ................................... 57 4.2.1 Application of TQ-ZCT-RN in HERIC Topology ......... 57 4.2.2 Operation Principle ................................... 58 4.2.3 Performance Analysis ................................ 63 4.2.4 Experimental Verification ............................. 66 4.3 SLF-H6-FPF Inverter ....................................... 69 4.3.1 Application of TQ-ZCT-RN in H6 Topology ............. 69 4.3.2 Operation Principle ................................... 70 4.3.3 Experimental Verification ............................. 75 4.4 ZCT-H5-FPF Inverter ....................................... 77 4.4.1 Application of TQ-ZCT-RN in H5 Topology ............. 77 4.4.2 Operation Principle ................................... 79 4.4.3 Experimental Verification ............................. 88 References ..................................................... 94 5 Zero-Voltage-Transition TLIs with Single-Quadrant Resonance Networks ...................................................... 95 5.1 ZVT Trajectory and Implementation Cells ..................... 95 5.2 ZVT-HERIC Inverter ....................................... 97 5.2.1 Derivation of ZVT-HERIC Topology ................... 97 5.2.2 Operation Principle ................................... 98 5.2.3 Conditions for Achieving ZVT ......................... 102 5.2.4 Parameter Design of Resonant Components .............. 103 5.2.5 Experimental Verification ............................. 104 5.3 ZVT-H5 Inverter ........................................... 110 Contents vii 5.3.1 Derivation of ZVT-H5 Topology ....................... 110 5.3.2 Operation Principle ................................... 111 5.3.3 Experimental Verification ............................. 115 5.4 ZVT-H6 Inverter ........................................... 118 5.4.1 Derivation of ZVT-H6 Topology ....................... 118 5.4.2 Operation Principle ................................... 119 5.4.3 Experimental Verification ............................. 123 References ..................................................... 129 6 Zero-Voltage-Transition TLIs with Two-Quadrant Resonance Networks ...................................................... 131 6.1 Two-Quadrant ZVT Resonance Networks ...................... 131 6.1.1 New Equivalent Structure of ZVT Cells ................. 131 6.1.2 Derivation of TQ-ZVT-RN ............................ 133 6.2 ZVT-HERIC-FPF Inverter ................................... 134 6.2.1 Application of TQ-ZVT-RN in HERIC Topology ......... 134 6.2.2 Operation Principle ................................... 136 6.2.3 Performance Analysis ................................ 140 6.2.4 Experimental Verification ............................. 143 6.3 ZVT-H6-FPF Inverter ....................................... 150 6.3.1 Application of TQ-ZVT-RN in H6 Topology ............. 150 6.3.2 Operation Principle ................................... 152 6.3.3 Experimental Verification ............................. 155 References ..................................................... 162 Chapter 1 Introduction Abstract Soft-switching technology can reduce switching loss and improve switching frequency of inverters. In this chapter, the conventional soft-switching implementation methods of inverters are reviewed at first, and then a new soft- switching inverter architecture is presented by means of the technical characteristics of non-isolated photovoltaic grid-connected inverter. · · Keywords Transformerless inverter Soft-switching configuration Resonant · · DC-link inverter Resonant pole inverter Freewheeling resonance tank inverter 1.1 Development History of Soft-Switching Inverters The concept of soft switching was firstly proposed by Professor Fred C. Lee, who is an internationally renowned power electronics expert, in the early 1980s. Nowadays, soft-switching techniques have been widely used in DC-DC converter applications [1]. However, when soft switching was transplanted into the inverter, there were considerable difficulties, for example, the interaction of multiple resonant processes makes the circuit difficult to work. Until the late 1980s, Professor Divan of the Univer- sity of Wisconsin (now Georgia Institute of Technology) proposed the landmark resonant DC-link inverter (RDCLI) [2] and resonant pole inverter (RPI) [3], which open up new ideas for the research of converter soft-switching technology, as shown in Fig. 1.1 [2–22]. After more than 30 years, researchers have proposed various types of inverter soft-switching improved topologies based on basic RDCLI and freewheeling RPI, and have some applications in isolated systems and independent systems [23]. With the rapid increase in the demand for grid-connected renewable energy, such photovoltaic grid-connected systems require higher conversion efficiency and lower costs to reduce the cost of electricity and the initial investment. A photovoltaic power generation system based on Transformerless Grid-Connected Inverter (TLI) is widely used in distributed photovoltaic power generation. In the TLI system, the photovoltaic array is electrically connected to the power grid. At the same time, the large-area photovoltaic array forms a large parasitic capacitance to the ground. Thus, a circuit with a lower impedance is formed for the common-mode voltage source of the switching frequency scale, and there is a larger common-mode current © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 1 H. Xiao et al., High-Frequency Soft-Switching Transformerless Grid-Connected Inverters, CPSS Power Electronics Series, https://doi.org/10.1007/978-981-19-3038-6_1 2 1 Introduction Soft-switching inverter Resonant DC link Resonant pole Freewheeling resonance inverter (RDCLI) inverter (RPI) tank inverter (FRTI) Parallel RDCLI Series RDCLI Parallel RPI Series RPI Zero-Voltage Zero-current FRTI FRTI CPoRnvDeCntLioI[n4]a l CoRnDveCnLtiIo[8n]al ARCPI[15] ConRvePnIt[9i]o nal ZVT-HERIC[20] ZCS-HERIC[22] Paper[5] ACRDCLI[9] ZCT-PWM[12] ZVT-PWM[16] Auxiliary ZVT-H5[21] ZCS-H5[22] diode RPI[19] QImRpDrCovLeId[2] QRDCLI[6] MAinCimRuDmC vLoIl[t10a]g e Δ-Snubber[13] Y-Snubber[17] ZVT-H6-I[21] ZCS-H6-I[22] Double coupled Transformer ZVT-H6-II[21] ZCS-H6-II[22] QIPmRpDroCvLeId[ 3] QPRDCLI[7] ACCoRmDpCoLsiIt[e11 ] inductRoPr Ia[u14x] iliary auRxPiIli[a18r]y Fig. 1.1 Technology tree of soft-switching inverters (leakage current) [3]. This leakage current will endanger the safety of personnel and equipment. Therefore, TLI products sold on the market must comply with leakage current standards, such as VDE 0126-1-1, IEEE 1547, etc. When the RDCLI and RPI are directly applied to TLI structure, the high-frequency time-varying common-mode voltage may act on the parasitic capacitance, resulting in the leakage current which may exceed the allowable range [24]. As a result, if we want to use soft-switching technology in TLI, we must avoid generating common- mode voltages. While the common-mode voltage of RDCLI and RPI soft-switching inverter topologies cannot be kept constant. In other words, if it is forced to change the drive timing of a constant common-mode voltage, the working timing of their resonant network will be destroyed, and the soft-switching operation will be lost. The Southeast University team proposed a freewheeling resonance tank inverter (FRTI) [22], as shown in the third branch of Fig. 1.1, and successfully introduced two types of soft-switching concepts of zero-current transition (ZCT) and zero-voltage transition (ZVT) into the inverter architecture. However, the soft switching of high-frequency tube can only be realized under the condition of unit power factor. Therefore, the team further improved the FRTI architecture, constructed a topological architecture that can support the dual-quadrant resonant network, and achieving the full power factor of the high-frequency switch tube soft-switching operation. This article will discuss the TLI soft-switching technology in detail based on the FRTI architecture.