模块化多电平换流器单极接地故障电流计算

Pole-to-ground Fault Current Calculation For Modular Multilevel Converter

基于模块化多电平换流器的直流系统的单极接地故障是一种常见的故障类型,接地故障电流暂态特性的分析对于故障检测、保护设置、系统参数的进一步优化都具有非常重要的工程实际意义。首先,在基于MMC拓扑结构的中压直流系统一定的调制策略基础上,通过分析故障电流的流通路径,对直流侧发生单极接地故障的故障特性进行了分析;然后,利用复频域分析法得到单极接地故障时的等效电路,通过计及故障时刻各相桥臂子模块投入数量,对各相桥臂在单极接地故障时刻的电容进行了等效,再根据叠加定理进行了换流器闭锁前的接地故障电流的理论推导;最后,得到单极接地故障电流值随故障时刻和交流侧接地电阻变化的规律,并通过PSCAD/EMTDC进行仿真计算,通过对比分析验证了接地故障电流理论计算的正确性。

Pole-to-ground fault of DC system based modular multilevel converter(MMC)is the most common type of fault.The analysis of the transient characteristics of the fault current has practical engineering significance for fault detection,protection setting and further optimization of system parameters.Firstly,based on the topological structure and modulation strategy of MMC of DC system,the fault current path is pointed out and the fault current characteristics of the pole-to-ground fault on the DC side are analyzed.Secondly,the equivalent circuit for pole-to-ground fault was obtained by using the complex frequency domain analysis method.Even the capacitance of each phase bridge arm at pole-to-ground fault is equivalent by counting the number of the sub-modules of each phase bridge arm at the fault time.Then the grounding fault current before IGBT blocking was derived theoretically according to the superposition theorem.Finally,the law of the change of pole-to-ground fault current with the fault time and the grounding resistance of the AC side is obtained.The correctness of the theoretical calculation of the grounding fault current is verified by comparative analysis with the simulation calculation of PSCAD/EMTDC.