MMC-HVDC交流侧不对称故障特性分析与保护策略

Characteristics Analysis of MMC-HVDC AC Asymmetric Fault and Protection Strategy

为研究模块化多电平换流器(MMC)交流侧不平衡故障机制及其针对性的保护策略,提升系统运行稳定可靠性,分离交流量的正序和负序分量,对三相电网电压不平衡故障下MMC-HVDC系统数学建模,分析其交流、直流电压及子模块电容电压、内部电流的变化过程,提出了一种以抑制交流侧负序电流为目标的MMC交流侧不平衡故障保护控制策略。以单相接地故障为例,基于电磁暂态仿真软件平台PSCAD/EMTDC进行仿真分析,结果显示负序电压补偿控制能够显著减小MMC内部电流的交流测馈入分量,减小子模块电压的波动范围,保证了系统的持续运行能力。

To study MMC AC unbalance fault mechanism and the corresponding protection strategy with the purpose to improve the stability and reliability of the operation system and to separate positive sequence and negative sequence component of AC,the mathematical model of MMC-HVDC system is established. Then its fault features under threephase voltage unbalance fault are analyzed. The fault features include the changing processes of AC,DC,SM capacitance voltage and the internal current. Finally,after single-phase ground fault has been simulated,based on the electromagnetic transient simulation software PSCAD / EMTDC,this paper proposes a fault protection control strategy for MMC under AC unbalance. The goal of the proposed strategy is to restrain the negative sequence current of the AC side. The simulation proves that the proposed control strategy can markedly diminish the circulating current and reduce the capacitance voltage range of MMC component,and can ensure the continuous operation of the system.