LCC-MMC型混合直流配电系统线路保护方案

Line Protection Scheme for Hybrid LCC-MMC Type DC Distribution System

换相型换流器-模块化多电平换流器(LCC-MMC)型混合直流配电系统发生双极短路故障时,有效故障暂态信息少,故障特征量单一,难以可靠地区分故障边界。基于此,该文提出一种适用于LCC-MMC型混合直流配电系统双极短路故障的保护方案。钳位双子模块的模块化多电平换流器(CDSM-MMC)和双有源全桥变换器(DAB)直流变压器故障闭锁后,结合电网换相换流器(LCC)提供稳态故障电流的典型特征,利用线路两端正极故障电流比值识别区内外故障,基于故障回路串联特性,演绎了线路两端正极稳态故障电流与LCC注入的正极稳态故障电流之间的关系,解析了故障距离,实现了故障精确定位,解决了故障边界模糊的问题。在PSCAD/EMTDC仿真平台上搭建LCC-MMC型混合直流配电系统模型。仿真分析表明,该方案能够可靠地区分故障边界,故障定位精确,较好地满足直流配电系统对保护可靠性和选择性的要求。

When LCC-MMC type hybrid DC distribution system has a pole-to-pole fault,the effective fault transient information is rare,and the fault feature quantity is not obvious,which make it difficult to reliably distinguish the fault boundary.Based on this,this paper proposes a protection scheme for pole-to-pole faults in LCC-MMC type hybrid DC distribution system.After CDSM-MMC and DAB dc transformer are blocked,combined with the typical characteristics that LCC provides the steady-state fault current,the ratio of the positive currents at two ends of line is used to identify the internal and external faults.Based on the series fault circuits,the relationship among the positive steady-state fault currents at both ends of the line and the positive steady-state fault current injected by LCC is deduced and the fault distance is obtained,which can accurately locate the fault positions and solve the problem of fuzzy fault boundary.The LCC-MMC type hybrid DC distribution system model is built in the PSCAD/EMTDC simulation platform.The simulation analyses show that the protection scheme can reliably distinguish fault boundaries,locate the fault position accurately and better satisfy the requirements of DC system for protection reliability and selectivity.