基于附加级联陷波滤波器的MMC-HVDC多频段谐振抑制策略

针对基于模块化多电平换流器（MMC）的柔性直流输电系统（MMC-HVDC）存在的中高频谐振问题，建立了MMC交流侧阻抗模型，分析了MMC呈现负阻尼特性的关键因素，即延时、电压前馈环节是主导MMC中高频段呈现负阻尼特性的主要原因，功率外环对中频段阻尼特性有较大的影响。对此，提出了附加级联陷波滤波器配置方法以最大限度地衰减电压前馈和功率外环对MMC的阻尼特性影响，在此基础上，针对正负序控制器引发的阻抗波动性问题提出了附加阻尼反馈环节和内环附加级联陷波滤波器2种抑制策略消除特定多频段的谐振风险。最后根据奈奎斯特判据分析了采用抑制策略的MMC与电网交互的谐振稳定性，并在电磁仿真软件中验证了理论分析和抑制方法的正确性与有效性。

Multi-band resonance suppression strategy for MMC-HVDC based on additional cascaded notch filters

Aiming at the medium and high frequency resonance problem existed in modular multilevel converter based high voltage direct current transmission system(MMC-HVDC),the AC-side impedance model of MMC is established. And the key factors of negative damping characteristics of MMC are analyzed, that is, the delay, voltage feedforward link are the main reasons for the negative damping characteristics of the dominant MMC in the medium and high frequency band, and the power outer loop has a greater impact on the damping characteristics of the middle frequency band. In this regard, an additional cascaded notch filter configuration method is proposed to minimize the influence of voltage feedforward and power outer loop on the damping characteristics of MMC. Based on this, two suppression strategies, i. e. the additional damping feedback link and the additional cascaded notch filter in the inner loop, are proposed to eliminate the resonance risk of specific multi-band for the impedance volatility caused by positive and negative sequence controllers. Finally, the resonance stability of the MMC with grid interaction using the suppression strategy is analyzed according to the Nyquist criterion, and the correctness and effectiveness of the theoretical analysis and the suppression method are verified in the electromagnetic simulation software.