含MMC的交直流输电系统短路电流统一求解方法

Unified solution method of short circuit current for AC/DC transmission system with MMC

针对含模块化多电平换流器(MMC)的交直流输电系统短路电流水平校核问题,在考虑MMC的运行方式和控制系统的基础上,建立了MMC交流侧故障模型。在对比分析了同步机电源和MMC输出短路电流的机理后,通过近似求解并网点(PCC)处电压将MMC交流侧故障模型简化为电流源模型以实现PCC处电压和MMC输出电流之间的解耦。对支路进行合理编号并筛选出电源支路和待求短路电流所在无源支路,基于电网络理论将联络节点构成的无源网络用混合参数表征,经推导得到了含MMC的电网短路电流计算的统一求解方法。不同工况下的仿真结果表明,通过建立各控制策略下的MMC交流侧故障模型,所提算法能准确统一求解不同MMC交流侧故障下的短路电流,可用于含MMC的交直流输电系统的设备选型和保护系统设计。

In view of the checking for short circuit current level of AC/DC transmission system including MMC(Modular Multilevel Converter),the fault model at MMC AC-side is established based on considering the operation mode and control system of MMC.After comparing the mechanism of short circuit current output by synchronous generators as well as MMC to realize the decoupling between the voltage at PCC(Point of Common Coupling) and the output current by MMC,the fault model at MMC AC-side is simplified to a current source by approximate solving the voltage at PCC.After reasonably numbering the branches,screening out the source branches,and the passive branches where the short circuit current is to be solved,the passive network composed of contact nodes is characterized by hybrid parameters based on the electrical network theory.Through derivation,the analytical expression of short circuit current for the power grid including MMC is obtained.The simulative results under different operating modes show that the proposed algorithm can accurately solve the short circuit current under different AC-side faults of MMC by establishing the fault models at MMC AC-side under different control strategies,and it can be used for equipment selection and protection system design of AC/DC transmission system with MMC.