MMC-MTDC系统直流单极对地短路故障保护策略

直流侧故障保护是基于模块化多电平换流器(MMC)的多端柔性直流输电(MTDC)系统的关键问题。现有文献主要对直流双极短路故障展开研究,而直流单极接地故障同样可能对系统安全运行产生严重影响。首先针对不同的换流器接地方式,分析半桥型MMC-MTDC单极对地短路故障特性,指出交流侧低阻抗接地方式下存在的问题,为实际工程接地阻抗选择提供一定参考。利用全桥型MMC的短路电流清除能力,提出一种单极对地短路故障快速恢复保护策略,能够在交流侧低阻抗接地方式下避免交流断路器跳闸。PSCAD/EMTDC仿真结果证明了故障特性分析的正确性和所提出的故障保护策略的有效性。

Pole-to-Ground DC Fault Protection of MMC-MTDC Systems

DC fault protection is a key issue of modular multilevel converter (MMC) based multi-terminal high voltage direct current (MTDC) transmission systems. Most of the existing literatures focus on the pole-to-pole DC short circuit fault. But the pole-to-ground fault also threatens the system security in some conditions. The fault characteristics of the half-bridge MMC-MTDC system is analyzed, adopting with AC and DC grounding modes, respectively. The grounding resistance is also discussed in this paper. Then, based on the capability of the fault current clearance of the full-bridge MMC, this paper proposed a pole-to-ground DC fault protection strategy to restore power transmission quickly. This method can avoid cutting off the AC and DC systems. The theory analysis and the proposed strategy are demonstrated by the PSCAD/EMTDC simulation.