交流系统短路故障下MMC对短路电流的影响及抑制策略

基于模块化多电平换流器的高压直流输电系统(MMC-HVDC)接入交流系统可能会对交流断路器清除短路故障造成影响。基于MMC的拓扑结构和控制策略，分析了交流系统短路故障下MMC对交流断路器的影响。然后，研究了交流系统发生对称短路故障时，MMC的运行工况对短路电流的影响，发现MMC对短路电流的贡献主要来源于MMC向交流系统注入的无功功率。接着，研究了交流系统发生非对称短路故障时，MMC在不同运行工况下贡献的三序短路电流的计算方法，得出MMC阀侧零序和负序电流为0，阀侧正序电流是三相对称的且大小由运行工况决定的结论。最后，提出了交流系统对称短路和非对称短路故障下抑制MMC贡献的短路电流的控制方法，并通过PSCAD/EMTDC仿真验证了所得结论的正确性以及控制方法的有效性。

Influence analysis and control strategy of MMC on AC short circuit current under short circuit fault of AC system

The MMC-HVDC(Modular Multilevel Converter based High Voltage Direct Current transmission system) affects the AC circuit breaker to clear the short circuit fault. Firstly, based on the topology and control strategy of MMC, the impact of MMC on the AC circuit breaker under short circuit fault of the AC system are analyzed. Secondly, the influence of the operating conditions of MMC on the short circuit current under a symmetric short circuit fault of the AC system is studied, which shows that the short circuit current contributed by MMC is mainly due to the reactive power injected into the AC system by MMC. Then the calculation method of the three-sequence short circuit current contributed by MMC under different operating conditions when an asymmetric short circuit fault occurs in the AC system is proposed. It is concluded that the zero-and negative-sequence currents on the valve side of MMC are zero, and the three-phase symme-trical positive-sequence currents are determined by the operating conditions of MMC. Finally, a control strategy for reducing the short circuit current contributed by MMC under symmetric and asymmetric short circuit faults of the AC systems is proposed. And the correctness of the conclusion and the effectiveness of the control strategy are verified by PSCAD/EMTDC simulation.