柔直电网拓扑对故障电流的影响机理分析

Influence mechanism of MMC-HVDC grid topology on fault current

柔性直流(柔直)电网线路故障严重威胁电力系统的安全稳定运行,而柔直电网拓扑对故障电流影响显著。文中首先分析不同接线方式柔直电网分别发生单极接地故障、极间短路故障后,放电电流的主要流通路径。然后,基于频域分析方法,分析得出故障电流主要受拓扑等值电感参数影响,并提出采用简化指标k评估显著影响故障电流的拓扑范围及换流站数目。结果表明,不同接线方式柔直电网分别发生单极接地故障、极间短路故障时,拓扑中各换流站放电程度取决于指标k,k越大换流站放电程度越大,反之则越小。最后,基于PSCAD仿真平台分别搭建五端伪双极及五端真双极系统进行验证,结果表明,所提故障电流高频分析方法及简化指标均正确有效。

The line fault of the modular multilevel converter based high voltage direct current(MMC-HVDC)grid seriously threatens the safe and stable operation of the power system,and the MMC-HVDC grid topology has a significant impact on the fault current.The main flow paths of the discharge current are analyzed when the single-pole grounding fault and the inter-pole short-circuit fault occur in the MMC-HVDC grid with different wiring methods.Then,based on the frequency domain analysis method,it is concluded that the fault current is mainly affected by the topological equivalent inductance parameters,and a simplified index k is proposed to evaluate the topology range and the number of converter stations that significantly affect the fault current.When the single-pole grounding fault and the inter-pole short-circuit fault occur in the power grid,the discharge degree of each converter station in the topology depends on the index k.The larger the k,the greater the discharge degree of the converter station.The smaller the k,the smaller the discharge degree of the converter station.Finally,the five-terminal pseudo-bipolar and five-terminal true bipolar systems are built on the PSCAD simulation platform for verification.The results show that the proposed high-frequency analysis method and simplified index of fault current are correct and effective.