基于辅助电路的MMC-HVDC直流故障处理策略

直流线路故障是基于模块化多电平换流器的高压直流输电(MMC-HVDC)系统必须解决的关键问题。文中提出一种基于辅助电路的直流故障处理策略,即双向晶闸管与开关型零损耗限流装置相配合的保护方案。首先分析了直流故障电流自然衰减的直流保护原理及现有方案的缺陷,进而提出采用双向晶闸管代替背靠背晶闸管集中配置在交流侧的方法来简化其控制回路;通过与开关型零损耗限流装置相配合,并对限流电抗器进行合理设计,能够使保护在不增加运行损耗的同时具有快速抑制短路电流的能力,降低清除直流故障时对交流系统长时间的冲击。此外,进一步提出相应的故障检测及恢复策略。最后,基于PSCAD仿真平台验证了所述保护方案的有效性。

Auxiliary Equipment Based Processing Strategy for MMC-HVDC DC Faults

The DC-link fault is a key issue for the flexible high-voltage direct current system using modular multilevel converter(MMC-HVDC). An auxiliary equipment based processing strategy for MMC-HVDC DC faults is proposed, namely, a novel scheme by bidirectional thyristors in collaboration with a breaker-type zero-loss fault current limiter. The DC-protections based on natural decay of the fault DC current and their shortcomings are analyzed first. It is then proposed that the bidirectional thyristors rather than back-to-back ones are configured and controlled on the AC-side to simplify the control loop. The bidirectional thyristors are controlled to cooperate with the appropriately designed breaker-type zero-loss fault current limiter, which can possess fast current limiting ability while reducing the long short-circuit current rush to AC system during the clearance of the DC-link fault. And the corresponding DC-fault detection and recovery strategy is presented. PSCAD based simulation results finally verify the validity of the proposed protection scheme. This work is supported by National Natural Science Foundation of China(No. 51577072).