MMC-HVDC系统结构对多端直流电网故障的影响分析

Impact Analysis of MMC-HVDC System Topology on Multi-terminal DC Network Faults

主要针对基于MMC的多端直流输电网直流故障特性进行研究。首先,对不同系统结构下换流站的稳态运行特性及短路故障电流路径进行研究,提出了不同MMC-HVDC系统结构直流接地故障电流路径的通用分析方法;然后,基于上述方法分析了不同接地方案对故障电流的影响,并提出了一种多端直流系统直流侧接地方案确定分析方法;最后,通过仿真模型对一个5端直流电网在不同系统结构下的接地与非接地直流故障响应进行了比较分析。研究结果说明了伪双极系统具有最好的单极故障电流特性,而直接接地系统受单极故障的影响最大;同时,仿真结果也说明了直流电抗对所有系统结构下的所有直流故障方式均具有良好的改善作用。

DC fault characteristics of multi-terminal HVDC based on MMC were studied.Firstly,a general analysis method of DC ground fault current paths for different MMC-HVDC system structures was proposed based on the steady-state operating characteristics and short-circuit fault current paths analysis of MMC converters under different system structures.Then,according to the above methodology,the influence of different grounding schemes on the fault current was investigated,and a method for determining the DC grounding scheme for a multi-terminal DC system was proposed.At last,a comparative analysis for the DC fault current responses of a 5-terminal DC network working under different system structures was carried out.The analyzed results show that the symmetric monopole system has the best pole-to-ground fault current characteristics,and the direct grounding system is most affected by the unipolar fault.At the same time,the simulation results also show that the DC reactors could improve the DC fault current characteristics in all of the DC fault types and MMC-HVDC system structures.