摘要
随着模块化多电平换流器直流输电(modular multilevel converter based HVDC,MMC-HVDC)的快速发展,远距离大容量架空线直流输电系统随之出现。相比于电缆线路,架空线输电易发生短路、闪络等瞬时故障,必须采取相应措施限制故障电流,避免系统停运。针对架空线真双极MMC-HVDC系统,分别从交流系统和换流阀的角度分析架空线路单极接地故障的等值电路模型和故障特性,推导故障电流的解析表达式。提出了一种新型故障限流模块,可有效抑制闭锁后短路电流幅值。依靠该限流模块的限流能力,设计了换流站快速重启策略。仿真结果证明,该限流方案可有效限制桥臂电流的大小及上升速率,消除系统交流侧及换流器内部续流二极管的过流危害,减小直流断路器的动作难度,加速故障极换流站重启,减少系统停运时间。
With the rapid development of the modular multilevel converter based HVDC system, the HVDC system with the long distance bulk power overhead line transmission appears. Compared with the cable line transmission, the overhead line is prone to happen short circuit faults such as flashover and other transient fault. Appropriate measures must be taken to limit the fault current and avoid system outage. In this paper, the equivalent circuit model was built to analyze the single-pole-to-earth fault characteristics form the AC system and the converter respectively. The math analytic expression of fault current was derived. A new fault current limiting module has been proposed, which effectively suppress the circuit current amplitude. According to the current limiting capability of the current limiting module, a fast converter restart strategy has been designed. The simulation results show that the current limiting scheme can effectively limit the fault current, eliminate the overcurrent hazard of the AC system and the free-wheeling diode inside the converter, reduce the operation difficulty of DC breaker, accelerate the restart of the fault pole converter, reduce the system outage time.
引文
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