基于离散模型的柔性直流电网短路电流计算方法

Short-circuit Current Calculation Method for VSC-HVDC Grid Based on Discrete Model

为计算柔性直流电网故障后的短路电流,提出基于离散模型的柔性直流电网短路电流数值计算方法。针对基于模块化多电平换流器的柔性直流电网,分析直流侧短路故障后的等效电路;建立基于后退欧拉法和梯形积分法的换流器电感、电容和线路的离散化模型,以及不同故障类型下换流站的离散化模型;在此基础上,设计直流电网不同类型故障电流数值求解算法。基于RT-lab平台搭建四端柔性直流电网仿真模型,对比分析了所提出方法的求解计算数值与详细模型仿真结果。结果表明所提算法能够准确获得故障电流值,与详细模型仿真结果相比误差小于5.5%。

To calculate the short-circuit current of voltage source converter based high voltage direct current(VSCHVDC)grid under fault,a numerical calculation method for the short-circuit current of VSC-HVDC grid based on a discrete model is proposed.For the VSC-HVDC grid based on a modular multilevel converter(MMC),the equivalent circuit after the DC short-circuit fault is analyzed.Based on the Backward Euler Method and the Trapezoidal Rule,the discrete models of the converter’s inductance and capacitor as well as lines are established.In addition,the discrete model of a converter station under different types of fault is built.On this basis,the numerical solution algorithm for different types of fault current in the DC grid is designed.On the RT-lab platform,the simulation model of a four-terminal VSCHVDC grid is constructed,and the calculation values obtained using the proposed numerical solution algorithm and the simulation results of a detailed model are compared and analyzed,indicating that the fault current value can be accurately obtained using the proposed algorithm,with a relative error of less than 5.5%in comparison to the simulation results.