基于MMC的中压直流配电网极间短路故障保护策略

近年来基于模块化多电平换流器(MMC)的直流配电网得到快速发展,但因其直流线路极间短路电流上升速度快,电力电子器件耐流能力差等原因,直流侧故障保护成为了亟需解决的问题。针对这一问题,考虑半桥型MMC(HBMMC)和全桥型MMC(FBMMC)2种不同的拓扑结构,分别分析中压直流线路极间短路情况下的故障特性并推导了故障电压电流的解析表达式。对于HBMMC提出一种桥臂限流模块和直流断路器配合的保护策略,解决了故障电流衰减缓慢和稳态电流过大的问题,降低了对直流断路器开断能力的要求。利用FBMMC子模块的故障电流自清除能力,提出一种改进的基于换流器解锁的快速恢复保护策略,减少瞬时性故障的系统停运时间。最后结合实际工程参数,在PSCAD/EMTDC仿真平台验证了保护策略的有效性和实用性。

Bipolar short circuit protection strategy for MMC based medium voltage DC distribution network

In recent years, the DC distribution network based on MMC is developing rapidly. However, DC side fault protection has become an urgent problem because of the sharply rising overcurrent generated by short circuit and the poor overcurrent capacity of power electronics. Considering the two different topologies of half-bridge and full-bridge MMC, the fault characteristics are analyzed and the analytical expressions of fault voltage and current are derived respectively when a bipolar short circuit occurs on medium voltage DC lines. For the half-bridge MMC, a protection strategy based on bridge arm current-limiting module and DC circuit breaker is proposed, which solves the problem of slow fault current attenuation and excessive steady current, and thus reduces the requirement for the breaking capacity of the DC circuit breaker. Based on the fault current self-clearing capability of the full-bridge MMC sub-module, an improved fast recovery protection strategy is proposed to reduce the system outage time by unlocking the MMC. Finally, the PSCAD/EMTDC simulation results prove the effectiveness and practicability of the protection strategy based on the actual engineering parameters.