Leakage Current Suppression and DC Voltage Balance Control for Non-Isolated Hybrid Three-Level Flexible Power Flow Converter
Bao Mingjun1, He Jinwei1, Zhang Chenyu2, Yuan Yubo2, Wang Chengshan1
1. School of Electrical and Information Engineering Tianjin University Tianjin 300072 China; 2. State Grid Jiangsu Electric Power Research Institute Nanjing 211103 China
Abstract：Non-isolated flexible current transfer devices face three challenges in engineering applications. (1) Leakage current suppression difficulty. Due to the lack of a physical isolation layer, the high-frequency switching action generated by the common-mode voltage and the system-to-ground parasitic capacitance can form a resonant loop, triggering leakage currents at the ampere level. (2) The DC voltage multi-source perturbation is significant. The coupling of power mutation, impedance network resonance, and other multi- physical fields exacerbates the risk of DC bus voltage instability. (3) Strong coupling of multi-objective control, such as the power dynamic response, leakage current amplitude, midpoint potential equilibrium, redundant vector selection, and the voltage loop bandwidth. This paper proposes a three-phase, three-wire and a three-phase, four-wire hybrid three-level flexible current transfer device. A direct closed-loop regulation suppression method of common-mode leakage current and a DC voltage balance control strategy are developed. Firstly, the common-mode equivalent circuit model of the non-isolated hybrid three-level flexible trend-switching device is established. The main components of the common-mode leakage current are the third and ninth harmonics. A direct closed-loop suppression strategy is proposed for the characteristic subharmonic components of the common mode leakage current. Secondly, an online estimation method is proposed for the low-frequency eigencomponent of the diode clamping current. A high degree of DC voltage equalization is achieved through the active harmonic injection of the midline current on the rectifier side. The experimental results show that the proposed method efficiently suppresses common-mode leakage current. The inverter-side grid current is close to sinusoidal, with a total harmonic distortion (THD) of 2.64%. As the rectifier-side converter needs to balance the DC bus voltage through midline current control, the rectifier-side current distortion rate increases (THD=4.64%). The peak common-mode leakage current is reduced to 0.25 A, approximately 83% lower than that of the conventional control system. In addition, through DC voltage balance control, diode clamping current, and common-mode leakage current feed-forward compensation, the DC voltage deviation is 2.53 V, a 50% decrease compared to the traditional control system. The following conclusions can be drawn. (1) The isolation transformer with high cost and large size is completely removed, which provides a new idea for the compact, flexible current transfer device. (2) The control objective of DC voltage balance and common mode leakage current suppression is realized, avoiding the strong coupling problem caused by vector selection. (3) The capacitor voltage fluctuation suppression provides an accurate estimation of the clamping current of the three-level converter.
包明骏, 何晋伟, 张宸宇, 袁宇波, 王成山. 非隔离混合型三电平柔性潮流转供装置的漏电流抑制和直流电压平衡控制策略[J]. 电工技术学报, 2026, 41(4): 1298-1310.
Bao Mingjun, He Jinwei, Zhang Chenyu, Yuan Yubo, Wang Chengshan. Leakage Current Suppression and DC Voltage Balance Control for Non-Isolated Hybrid Three-Level Flexible Power Flow Converter. Transactions of China Electrotechnical Society, 2026, 41(4): 1298-1310.
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2026, Vol. 41 
