三 电 平 变 流 器 中 点 电 位 波 动 与 关 联 谐 波 特 征 的 解 析 及 抑 制

As a mainstream topology in power-electronic source-load systems, the three-level neutral point clamped converter inherently exhibits third-harmonic fluctuation in the DC neutral-point potential, which causes pronounced low-order harmonic emission on the AC side and has become one of the major harmonic sources in renewable energy plants. In this paper, the impact of the output third-harmonic component on the neutral-point potential in the three-phase four-wire topology and the multi-frequency coupling relationship are incorporated into the analysis. First, a unified analytical fluctuation-loop model is established for various topologies, carrier-based modulation schemes, and output operating conditions, which enables correlation analysis and characteristic interpretation between neutral-point potential fluctuation and AC low-order harmonic emission. Then, the amplification effect and the amplification ranges of passive parameters on neutral-point potential fluctuation and harmonic-emission distortion are revealed, and improvement measures aimed at suppressing harmonic emission or neutral-point potential fluctuation are proposed based on the analytical model. The proposed suppression methods cover a range of typical operating conditions and are easy to implement in engineering. Experimental results validate the accuracy of the developed analytical model and the effectiveness of the proposed suppression methods.