基于MMC的两端TWBS-HVDC直流侧短路故障电流计算方法

基于三线双极结构的高压直流(TWBS-HVDC)输电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,文中提出了一种适用于两端TWBS-HVDC的直流侧短路故障电流计算方法。首先基于模块化多电平换流器(MMC)暂态等效电路建立两端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,为直流断路器选型和限流电抗器参数整定提供了可靠依据。

Current Calculation Method of Short-circuit Fault at DC Side for MMC Based Two-terminal TWBS-HVDC

The three-wire bipolar structure based high voltage direct current (TWBS-HVDC) transmission 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 improving line capacity. Aiming at the difference between TWBS-HVDC and bipolar DC system in connection ways, a current calculation method of short-circuit fault at DC side for two-terminal TWBS-HVDC system is proposed. Firstly, the transient equivalent model of TWBS-HVDC system is established based on modular multilevel converter (MMC) based transient equivalent circuit in the stage from different faults at DC side to the operation of DC breakers of lines. The number of independent circuits and the order of dynamic components in the transient equivalent circuit are taken as the standard, all DC faults are classified into three categories, and the state equations of each kind of fault are analyzed and deduced. The analytical expression of fault current is obtained by solving the eigenvalue and eigenvector of coefficient matrix in the state equation. Finally, a two-terminal TWBS-HVDC system simulation model is established in the MATLAB/Simulink digital simulation platform, and the simulation results validate the effectiveness and accuracy of the state equation solution method of short-circuit fault at the DC side of the proposed TWBS-HVDC system, which can provide a scientific basis for the selection of DC breakers and parameter setting of current limiting reactors.