混合多端直流输电系统故障线路识别方法

针对混合多端直流系统不同线路之间直接相连、无法依靠直流线路边界特性进行故障识别的问题，以乌东德三端混合直流示范工程为背景，研究了三端星型直流输电系统中汇流区的结构特点；并根据彼得逊法则和叠加定理得到了故障后汇流区两侧暂态电流行波的变化特征，发现电流行波经过汇流区后中低频段有大幅的衰减。因此，利用小波变换提取汇流区两侧故障电流行波的中低频段能量，并根据两侧小波能量的标准差构造故障识别判据，进而快速、可靠地识别故障线路。最后，基于仿真结果，验证了故障识别方法的正确性。

Fault Line Identification Method for Multi-terminal Hybrid DC Transmission System

To deal with the problem that the different lines of the multi-terminal hybrid DC system are directly connected and cannot rely on the characteristics of the DC line boundary for fault identification， the Wudongde three-terminal hybrid DC demonstration project is used as the background to study the confluence area of the three-terminal star-type HVDC transmission system. According to Peterson's law and superposition theorem， the variation characteristics of transient current traveling wave on both sides of the confluence region after fault are obtained. It is found that the current traveling wave passes through the confluence region and has a large attenuation in the middle and low frequency bands. Therefore， the wavelet transform is used to extract the low-frequency energy of the fault current traveling wave on both sides of the confluence region， and the fault identification criterion is constructed according to the standard deviation of the two-side wavelet energy， so that the fault line can be identified quickly and reliably. Finally， based on the simulation results， the correctness of the fault identification method is verified.