基于电流方向信息的直流配电网故障隔离方法

Current Direction Based Method of Fault Isolation of Four-Terminal DC Distribution Network

文章首先分析了基于模块化多电平换流器(modular multilevel converter,MMC)的多端直流配电系统线路短路故障的过程机理;研究了闭锁后换流器电容、网侧交流电源对故障点馈入的放电电流数学模型;提出了一种基于电流方向信息隔离直流线路短路故障的方法 ;该方法提出先闭锁后隔离故障的顺序,闭锁后送端换流站和受端换流站停止功率传输;此时系统直流线路只存在流向故障点的放电电流,因此非故障线路两端的电流方向一致,而故障线路的电流方向不一致;利用此特征可以在闭锁后极短时间内判定故障线路,结合保护判据识别故障类型,应用固态直流断路器快速隔离故障区域;在RTDS/RSCAD中搭建四端放射形直流配电网模型,仿真结果显示在不同故障类型下,相关直流断路器能在极短时间内动作,系统内其他直流断路器不会误动;换流器电容电压下降较少,可缩短下一步电容充电时间,快速恢复系统运行。

The paper analyses process mechanics of short circuit faults in a modular multilevel converters based multi-terminal dc distribution network; Then it has a research on the mathematical model about inverter capacitors and network side ac power to feed-in discharging currents at fault points after being locked; In final, the paper proposes an isolation method of de line fault, in terms of current directions. The method presents an order of faults isolation after being locked, and the sending converter station and the receiving end stop their power transfer; At the moment, the dc line of system only exists discharging currents flowing to fault point, resulting in the same current direction at both ends of the unfault line, whereas fault lines have different current directions; Using this feature can determine fault lines after atresia within a very short time, combined with the protection criterion to identify the fault type, and by the application of solid state dc circuit breaker quickly isolate fault zone. In RSCAD/RTDS, the paper builds four terminal radiate dc power distribution network model, and the simulation results show that under different fault types, corresponding dc circuit breakers can act in a very short time, without other dc circuit breakers mal-operation. Less inverter capacitor voltage drop, shortening the capacitor charging time, the system can fast recovery.