基于反向行波幅值比的对称单极柔性直流系统行波方向保护  

The Direction Protection Based on the Amplitude Ratio of the Backward Traveling Wave for the Symmetrical Monopole Flexible DC System

作　　者：李晔 李斌 刘晓明 何佳伟 贾冠龙 Li Ye;Li Bin;Liu Xiaoming;He Jiawei;Jia Guanlong(State Key Laboratory of Reliability and Intelligence of Electrical Equipment School of Electrical Engineering Hebei University of Technology,Tianjin,300132,China;Key Laboratory of Smart Grid of Ministry of Education School of Electrical and Information Engineering Tianjin University,Tianjin,300072,China)

机构地区：[1]省部共建电工装备可靠性与智能化国家重点实验室、河北工业大学电气工程学院,天津300132 [2]天津大学智能电网教育部重点实验室、天津大学电气自动化与信息工程学院,天津300072

出　　处：《电工技术学报》2023年第9期2418-2434,共17页Transactions of China Electrotechnical Society

基　　金：国家杰出青年科学基金(52025071);国家自然科学基金联合基金(U1866205)资助项目。

摘　　要：快速可靠的方向保护对直流线路保护研究具有重要意义。传统行波方向保护基于正反向行波幅值比识别故障方向,保护动作速度快且无需依赖线路边界,应用前景广阔。但研究发现,当对称单极运行的模块化多电平换流器柔性直流系统发生单极故障时,由于换流站各桥臂子模块投入数量的动态变化会导致直流侧等值阻抗不断变化,从而导致以行波反射系数为整定依据的传统行波方向保护失效。为此,该文提出不依赖线路边界且不受换流站控制响应影响的行波方向保护原理。首先,利用换流站直流出口直流电抗器两侧暂态电压幅值比识别故障是否发生于直流线路侧;然后,利用各条线路反向行波幅值比确定故障线路,有效地消除了换流站控制响应的影响;最后,通过大量的仿真算例充分验证了该文所提方向保护的优势和可行性。The flexible DC grid is considered as an important trend of the power system development in the future,with the advantages in large-scale renewable energy access,new urban power supply and so on.However,the DC fault propagation speed of the flexible DC grid is faster,which will damage the whole system in a few milliseconds.Therefore,the fast and reliable direction protection is of great significance for DC line protection.The traditional direction protection based on the amplitude ratio of the forward and backward traveling wave can identify the fault direction fast independent of the line boundary,which has a wide application prospect.However,for the symmetrical monopole flexible DC system,the traditional direction protection cannot identify the pole-to-ground fault direction,because the equivalent impedance of the converter is changing as the result of the dynamic change of the input quantity of the sub-modules.Therefore,a novel direction protection based on the traveling wave is proposed,which is independent of the line boundary and not affected by the converter control influence.Firstly,the basic principle of the traditional direction protection based on the ratio of the forward traveling wave and the backward traveling wave is introduced.And on this basis,the applicability in the symmetrical monopole flexible DC system is analyzed.For the symmetrical monopole flexible DC system,when the DC pole-to-ground fault occurs,the control response of the converter station will affect the DC fault characteristics,generating the additional fault traveling waves which cannot be accurately calculated.In this case,the traditional traveling wave based direction protection criterion cannot identify the forward and backward faults explicitly in the symmetrical monopole flexible DC system.According to the analysis of fault traveling wave propagation process,there is no backward traveling wave when the backward fault occurs.Therefore,the direction criterion based on the ratio of the backward traveling wave amplitude of each lin

关 键 词：柔性直流系统 对称单极运行 故障行波特性 行波方向保护 故障方向识别 

分 类 号：TM77[电气工程—电力系统及自动化]