多端柔性直流电网的故障定位方法

Fault Location Technique for Multi-Terminal VSC-HVDC System

多端柔性直流电网的故障定位技术是保障直流电网安全可靠运行的关键技术,以基于两电平电压源型变流器(two-level voltage source converter,two-level VSC)所组成的多端柔性直流电网为研究对象,采用先定区段再定位的思想研究其故障定位技术。由于受到故障回路和直流侧大电容的影响,故障区间和非故障区间变流器出口处直流电容的电压变化率(du/dt)不同,根据上述特征可以采用对比VSC出口侧直流电容放电电压变化率的方法来确定故障区段;故障区段确定后,利用短路故障所形成的放电回路推导出故障位置的计算公式,并将VSC直流电容的暂态电压录波数据进行分段计算来完成故障测距。在MATLAB/Simulink中搭建基于两电平VSC的多端柔性直流电网,并对所提出的方法进行仿真验证;同时将所提出的方法与已有的方法进行对比分析,验证所提出方法的可行性和有效性。

The fault location technique of multi-terminal flexible DC （MTDC） grid is one of the crucial techniques for the safe and reliable operation of DC power grid. This paper takes the MTDC grid based on two-level voltage source converter （VSC） as research object, and adopts the idea of ＂first predetermined section then position＂ to study its fault location technique. Under the impact of fault loop and big DC capacitor, the DC capacitor voltage change rate （du/dt） at converter outlet is different in fault region or non-fault region. Based on this characteristics, we can determine fault region by comparing the du/dt at VSC outlet. After the determination of fault region, we can use the discharge circuit formed by the short-circuit fault to derive the calculation formula of the fault position, and calculate the precise fault position by using recorded data of transient voltage of VSC DC capacitor. We build VSC-HVDC system in MATLAB/Simulink, simulate and verify the proposed method. At the same time, we compare the proposed method with the existing methods to verify the feasibility and effectiveness of the proposed method.