电力电子变压器中压直流端口单极接地故障特性研究

Research on Characteristics of Pole-to-Ground Fault in MV Power Electronic Transformer DC Port

针对电力电子变压器直流端口可能发生的单极接地短路进行故障分析。电力电子变压器直流端口一般有2种运行方式,包括单极金属回线接线和伪双极运行方式。不同运行方式下有不同的接地方式,不同的接地方式下也会有不同的故障特性。首先分析了单极金属回路运行方式下单极接地故障特性,给出定量的短路电流计算表达式,提出在接地电阻较小时,短路过程分为谐振阶段和反并联二极管续流阶段,接地电阻较大时,仅有谐振阶段;其次分析了伪双极运行方式下的单极接地故障特性,不论是端口空载还是带负载情况,整个短路过程都只有谐振阶段。PSCAD仿真结果验证了电力电子变压器直流端口的接地故障特性。

In this paper, fault analysis of pole-to-ground fault in DC port of power electronic transformer（PET） is carried out. The PET DC port usually has two operation modes, monopole ground loop and pseudo-bipolar operation mode. Different operation modes have different grounding modes, causing different fault characteristics. The characteristics of pole-to-ground fault under monopole ground loop mode are analyzed and quantitative expression of short circuit current is given. When ground resistance is small, the short-circuit process can be divided into resonance stage and anti-parallel-diode continuous flow stage. When the ground resistance is large, only the resonant stage exists. Then, the characteristics of monopole grounding fault under pseudo-bipolar operation mode are analyzed. It is concluded that whole short circuit process only has resonance stage. PSCAD simulation results verify the fault characteristics of PET DC port.