Non-isolated H10 three-phase inverter for leakage current suppression
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ORIGINAL ARTICLE
Non‑isolated H10 three‑phase inverter for leakage current suppression Haixiao Ma1 · Zhaixing Lan1 · Zefeng Chen1 Received: 31 March 2020 / Revised: 28 June 2020 / Accepted: 30 June 2020 © The Korean Institute of Power Electronics 2020
Abstract In recent years, an increasing amount of attention has been paid to non-isolated photovoltaic power generation systems, where leakage current suppression is one of the key issues to be addressed. In view of this problem, this paper proposes a novel ten-switch three-phase circuit that is referred to as an H10 inverter. This circuit is obtained by adding two isolating switches and a clamping circuit to the traditional three-phase inverter (H6 inverter). The working principle of the proposed system is analyzed. On the basis of the logic relationship between the common-mode voltage (CMV) and the switching states, a control strategy combining carrier modulation and logic operation is proposed. With this proposed control strategy, the H10 inverter can effectively reduce the variation of the CMV and improve the leakage current suppression. Finally, simulation and experimental platforms are built for the inverter system, and the obtained results are compared with those of a traditional three-phase inverter to verify the correctness of the theoretical analysis. Keywords Non-isolated photovoltaic power generation system · Leakage current · H10 inverter · Clamping circuit · Common-mode voltage (CMV)
1 Introduction Photovoltaic power generation is an important industry for the future of power and it has been an indispensable method for the adjustment of energy in many countries and regions [1–3]. In general, photovoltaic systems are equipped with power frequency or high frequency transformers to achieve power adjustment and electrical isolation. However, they suffer from the shortcomings of bulkiness and inefficiency [4–6]. Non-isolated photovoltaic inverters have been widely used in practical projects due to their small size, low cost and high efficiency [7]. However, their lack of electrical isolation can cause leakage current in the system, which results in electromagnetic interference, causes grid current distortion and endangers the safety of personnel and equipment [8–11]. According to the German VDE 0126-1-1 standard, the leakage current of photovoltaic systems cannot be higher than 300 mA [12], or it must be cut off within a specified time.
* Haixiao Ma [email protected] 1
College of Automation, Nanjing University of Posts and Telecommunications, Nanjing, China
Therefore, non-isolated inverters that can better restrain leakage current have become a research hotspot [13, 14]. In an effort to cope with the problems of leakage current, many insightful three-phase topologies have been reported. Freddy et al. [15] proposed a H7-type three-phase inverter. Since the negative DC bus of this topology is always in the conduction state, it provides a possible path for the leakage current to flow, which results in poor leakage current suppression capability. Rahi
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