基于伴随网络的直流电网短路电流计算方法

A Short-Circuit Current Calculation Method Based on Adjoint Network for DC Grid

直流线路发生短路故障后,子模块电容作为换流器闭锁前短路电流的主要贡献单元,其极快的放电速度,对直流电网的安全稳定运行提出了严峻考验,亟待开展直流电网短路电流计算方法的研究。首先采用梯形积分法对所建直流电网等效模型中的动态元件进行离散化,再通过改进节点法构建网络方程,迭代求得故障支路各时刻的短路电流,进而提出一种基于伴随网络的直流电网短路电流计算方法。在PSCAD/EMTDC软件中搭建四端双极环形直流电网模型进行仿真,根据直流线路发生不同类型故障的仿真结果,在计算精度和计算效率2个方面,将所提计算方法与典型的状态空间法进行比较,分析了2种方法的误差来源,验证了所提算法的有效性。

When a short-circuit fault occurs in a DC line,the sub-module capacitor is the main contribution unit for the short-circuit current before the blocking of the converter.Its extremely fast discharge speed poses a challenge to the safe and stable operation of DC grid.It is thus urgent to study the calculation method of the short-circuit current in DC grid.Firstly,the trapezoidal integration method is used to discretize the dynamic components in the established DC grid equivalent model.Then,the improved node method is used to construct the network equation,and the short-circuit current of the faulty branch is obtained through iteration.Furthermore,a new method is proposed to calculate the short-circuit current of DC grid based on adjoint network.A four-terminal real bipolar toroidal DC grid model is built in PSCAD/EMTDC software.According to the simulation results of different types of faults in DC lines,the proposed calculation method is compared with the typical state space method in terms of calculation accuracy and calculation efficiency.The error sources of the two methods are analyzed,and the effectiveness of the proposed algorithm is verified.