基于MMC的多端直流电网双极短路故障电流计算

Pole-to-pole short circuit current calculation of multi-terminal DC grid based on MMC

直流侧故障切除能力是衡量直流输电系统的重要指标。针对子模块采用半桥拓扑的模块化多电平换流器(MMC)直流侧发生双极短路故障的机理进行分析,定量研究了影响故障电流峰值的主要因素;并将结论延伸至多端直流电网,提出了不同电网拓扑和不同位置发生故障后10 ms内各换流站出口、线路电流的计算方法;在PSCAD/EMTDC仿真软件中搭建三端电磁暂态仿真模型,并将故障电流计算结果与仿真结果进行对比验证,结果表明所提计算方法具有一定的精度和速度,对直流电网规划、直流断路器选型具有一定的指导意义。

DC-side fault removal capability is an essential index for evaluating DC transmission systems. The mechanism of DC-side pole-to-pole short circuit fault in HBSM（ Half-Bridge Sub-Module）-based MMC-HVDC（ Modular Multilevel Converter based High Voltage Direct Current） system is analyzed,and the main factors affecting the peak value of fault current are studied quantitatively. Then,the conclusions are extended to the multi-terminal MMC system,and a calculation method for outlet current of each converter station and line current within 10 ms after faults is proposed,which is applicable for different power grid topologies and different fault locations. The electromagnetic transient simulation model of a three-terminal system is built in PSCAD/EMTDC simulation software,and the calculative results of fault current are compared with the simulative results. The results show that the proposed calculation method has a certain accuracy and speed,and has guiding significance for DC power grid planning and selection of DC circuit breakers.