基于三线双极结构的高压直流输电(three wires bipole structure based high voltage direct current,TWBS-HVDC)系统能够较大程度地发挥直流线路的输电能力,是一种实现交改直和线路增容改造的有效方式。针对TWBS-HVDC系统与双极直流系统在接线形式上的差异,本文提出了一种适用于TWBS-HVDC的直流侧短路故障电流计算方法。首先基于MMC暂态等效电路建立TWBS-HVDC在不同直流侧故障发生至线路直流断路器动作阶段的暂态等效模型。以暂态等效电路中独立回路数和动态元件阶数为标准,将所有直流故障归纳为3类,分析推导各类故障下的状态方程,通过求解状态方程中系数矩阵的特征值和特征向量得到故障电流解析表达式。最后在MATLAB/Simulink数字仿真平台中,搭建两端TWBS-HVDC模型进行仿真验证,结果验证了本文所提TWBS-HVDC直流侧短路故障状态方程求解法的准确性和有效性。
The three wires bipole structure based high voltage direct current (TWBS-HVDC) system can greatly enhance the transmission capacity of the DC lines, which has become an effective method for converting AC line into DC line and lines capacity improvement. Aiming at the difference between TWBS-HVDC and bipole direct current system in connection ways, a DC side short-circuit fault current calculation method for TWBS-HVDC system was proposed. Firstly, the transient equivalent model of TWBS-HVDC system was established based on MMC transient equivalent circuit. The number of independent circuits and the order of dynamic components in the transient equivalent circuit were taken as the standard, all DC faults were classified into three categories, and the state equations of each kind of fault was analyzed and deduced. The analytical expression of fault current was obtained by solving the eigenvalue and eigenvector of coefficient matrix in the state equation. Finally, a two-terminal TWBS-HVDC system simulation model was established in the MATLAB/Simulink digital simulation platform, and the simulation results validated the effectiveness and accuracy of the short-circuit fault state equation solution method on the DC side of the TWBS-HVDC system proposed in this paper, which can provide a scientific basis for the selection of system main circuit parameter and the setting of relay protection action time.