基于暂态电流的MMC-LVDC双极短路故障定位方法

随着分布式电源和直流负荷的大量接入,直流配电系统相较于交流系统更具优势。故障定位是直流配电网可靠、优质供电的关键支撑技术之一。分析了模块化多电平换流器(MMC)型柔性直流配电网双极短路故障暂态特性,提出了一种基于子模块闭锁后初始阶段暂态电流的故障精确定位方法,建立了双端MMC型柔性直流配电网的等效电路,推导了直流电流的时域表达式,构建包含故障距离和过渡电阻2个未知参数的时域方程组,并利用最小二乘法进行求解。该方法适用于不同接地方式。在PSCAD/EMTDC中搭建了双端柔性直流配电网模型。仿真结果验证了该方法的有效性、可靠性与准确性,针对两端换流站参数不对称和过渡电阻时变场景,所提方法也具有很高的定位精度。

Transient Current Based Fault Location Method of Pole-to-pole Short-circuit for Modular Multilevel Converter Low-voltage Direct Current

With the integration of large number of distributed power sources and DC loads, the DC distribution system has more advantages than AC system. Fault location is one of the key supporting technologies for reliable and high-quality power supply of DC distribution network. This paper analyzes the transient characteristics of the pole-to-pole short-circuit fault in the modular multilevel converter (MMC) based flexible DC distribution network and proposes a precise fault location method based on the transient current at the initial stage after the blocking of the sub modules. The equivalent circuit of two-terminal MMC based flexible DC distribution network is established. The time-domain expression of DC current is derived, the time-domain equations including two unknown parameters of fault distance and transition resistance are constructed, and the least square method is used to solve the equations. The method is suitable for different grounding modes. In PSCAD/EMTDC, a two-terminal flexible DC distribution network model is built. The simulation results verify the effectiveness, reliability and accuracy of the method. The proposed method also has high location accuracy for the scene of asymmetric parameters and time-varying transition resistance of converter stations at both terminals.