Self-Balance Mechanism Analysis of the Neutral Point Voltage in Three-Level Full Bridge DC-DC Converter with Flying Capacitors
Liu Peng, Chen Changsong, Duan Shanxu
State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 China
Abstract：The balance of the neutral point voltage is always an important issue for the three-level topologies, but the deep analysis about the neutral point voltage balance in the three-level full bridge (TLFB) DC-DC converter has not been provided in publications. Focusing on the TLFB converter, this paper provides the detailed mode operation analysis of the converter and reveals the cause of the unbalanced neutral point voltage. Moreover, the mechanism of the self-balance ability brought by the flying capacitors is explained in detail. First, the supply modes of three-level half bridge (TLHB) and TLFB converters without flying capacitors are compared. It is pointed out that in the case of inconsistent turn-off of the diagonal switches, an individual input capacitor will have to provide the load current, resulting in an offset of the neutral point voltage. Then the detailed mode operation of TLFB with flying capacitor has been provided when the diagonal switches turn off inconsistently, which proves that flying capacitors can relieve the drift of the neutral point voltage and further achieve the self-balance of the neutral point voltage. At last, the influence factor of the voltage drift in steady state has been analyzed. The specific expression has also been derived, which is another important design guidance for the TLFB converter. The feasibility of the proposed method is verified by the simulation and experimental results.
刘朋, 陈昌松, 段善旭. 带飞跨电容的三电平全桥直流变换器输入中点电压的自平衡分析[J]. 电工技术学报, 2018, 33(18): 4335-4344.
Liu Peng, Chen Changsong, Duan Shanxu. Self-Balance Mechanism Analysis of the Neutral Point Voltage in Three-Level Full Bridge DC-DC Converter with Flying Capacitors. Transactions of China Electrotechnical Society, 2018, 33(18): 4335-4344.
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2018, Vol. 33 
