电压源换流器直流侧短路故障特性分析

DC side short-circuit fault analysis of VSC

电压源换流器直流侧发生故障时,其故障电压电流变化迅速,对系统造成了严重威胁。针对这一问题,从电力电子层面深入分析了电压源换流器直流侧短路故障中最为严重的两极短路故障过程。将故障过程分为3个阶段,推导了电容放电阶段直流电压、电流表达式,分析了不控整流初始阶段存在的两种情况,对不控整流稳态阶段提出了采用开关函数计算短路电流的方法。最后通过PSCAD/EMTDC环境下±10 kV直流线路两极短路故障模型的仿真计算,对理论分析进行了验证。研究结果表明,两极短路故障后电路的响应情况与短路阻抗大小相关,短路阻抗较小时需要直流断路器在极短的时间内切除故障,短路阻抗较大时则可以利用交流侧的保护装置对直流侧电压、电流进行动态监测,实现直流侧短路故障的后备保护。

As the fault voltage and current change raptly in case of DC side fault of voltage source converter（VSC）, it＇s a serious threat to the whole system. Aiming at this problem, the mechanism of DC side short-circuit fault, which is the most serious DC side fault of VSC, was analyzed on power electronics level. The three stages of fault process were presented in detail. Firstly, fault voltage and current expressions of capacitor discharge stage were derived. Then, the existing two cases of the uncontrolled diode rectifier initial stage were elaborated further. Moreover, the calculation of short-circuit current of the uncontrolled diode rectifier stable stage using switch function was proposed as well. Finally, theoretical analysis of the short-circuit fault process was validated through the PSCAD/EMTDC simulation of ＋10 kV DC line. The results indicate that the response of the fault is related to the fault impedance closely. Quick removal of the fault needs to be done by DC circuit breaker instantly when the fault impedance is small, while backup protection could be obtained by dynamic monitoring voltages and currents in ac side using protection devices of ac side when the fault impedance is relatively large.