基于单端量的柔性直流电网故障识别方案

Single-ended Fast Fault Detection Scheme for MMC-based HVDC

直流线路故障的快速、可靠识别是基于架空线路的大容量、高电压柔性直流输电系统发展的关键技术之一,因而分析了模块化多电平换流器型高压直流系统直流线路短路故障后线路两端限流电抗器上的电压变化情况,提出了一套仅利用单端暂态量的柔性直流电网故障识别方案。该方案利用低压作为启动判据,利用限流电抗器上的电压变化率大小和极性确定故障区间,利用检测到的零模故障分量的多少确定故障极。在PSCAD搭建了张北四端柔性直流电网仿真模型,并考虑混合式直流断路器动作过程、过渡电阻、限流电抗器和桥臂电抗器大小等对保护方案性能的影响。仿真结果表明：所提出的保护方案能在各种情况下快速、准确识别故障,且无需通信,无需复杂的数据处理和分析,数据采样频率要求低,满足柔性直流输电系统对保护的要求。

The fast and reliable identification of direct current（DC） transmission line faults is one of the key technologies for the development of large capacity and high voltage flexible DC grid. So we proposed a single-ended fault detection scheme by analyzing voltage variation of the current limiting reactor after the DC line fault in MMC-base HVDC. In this scheme, the low voltage is used as the starting criterion, the fault zone is determined by the magnitude and polarity of the voltage change rate of the current limiting reactor, and the fault pole is confirmed through using zero sequence fault component. A Zhangbei test system is built in PSCAD, which considers the influence of hybrid DC circuit breakers, transition resistance, current limiting reactor, and arm reactor. The simulation results demonstrate that the proposed protection scheme can identify the fault quickly and accurately in all cases without communication, high sampling frequency, and sophisticated data analyses. The scheme can satisfy the protection requirements of MMC-HVDC.