基于桥臂电压控制的MMC直流短路主动限流方法

基于模块化多电平换流器(modular multilevel converter,MMC)的柔性直流输电系统直流短路后电流上升迅速且伴随大量的能量释放,为限制其故障电流,提出一种基于桥臂电压控制的MMC主动限流方法。根据故障电流影响因素分析,针对不同交流出口特性需求,设计了故障期间桥臂电压控制方法,通过减小桥臂电压直流分量降低直流出口电压,从而抑制故障电流上升率;考虑主动限流策略对交流电压及桥臂电流的影响,以MMC不闭锁为约束条件,设计了控制参数的选取原则,最后在四端直流电网中对该主动限流方法的限流效果及其对故障切除后功率恢复的影响进行了仿真分析。结果表明,所提主动限流方法能够有效限制短路电流,降低直流断路器的电流开断难度,且对故障切除后的功率恢复影响较小。

Active Current-limiting Method of MMC to Handle DC Short-circuit Based on Bridge Arm Voltage Control

The DC fault current of the voltage source converter HVDC(VSC-HVDC) based on MMC rises rapidly with accompanying high fault energy. In order to handle DC short-circuit in a VSC-HVDC system, an active current-limiting method of MMC based on the bridge arm voltage control is proposed. By analyzing influence factors of the fault current, the bridge arm voltage control is designed for different needs of AC system. And the DC component of the bridge arm voltage is cut down to reduce the DC voltage of MMC, then the fault current is limited. Considering the influence of the active current-limiting method on AC voltage and bridge arm currents, the selection principle of the control parameters is designed on the premise that MMC will not block. Finally, current-limiting effects of the active current-limiting method and its influence on power recovery after fault clearance are simulated and analyzed in four terminal DC grids. And the results show that the proposed method can limit the short-circuit current effectively, which alleviates the difficulty of DC circuit breaker on fault clearance and causes little effects on power recovery.