基于MMC主动限流的柔性直流配电网优化配合保护策略

Once a DC fault occurs on the flexible DC distribution network based on modular multilevel converter (MMC), the fault current will increase rapidly, threatening the security and stability of the DC grid. To restrain the DC fault current, an optimized coordination protection strategy based on a newly designed active current limiting control is proposed. This strategy limits the fault current by reducing the rising rate of the DC fault current and the speed of fault isolation, then reduce the breaking current of DC circuit breaker. Firstly, the active current limiting control is used to limit the fault current rising rate after a DC fault occurs; Next, the faulty line is quickly identified according to the single end current change rate characteristics; Then, the proposed optimized coordination protection strategy is further designed by means of a coordination between the rapid fault identification and the DCCB operation, and the fault protection time is reduced by adjusting the timing sequence. Finally, the effectiveness of the proposed strategy is verified by various simulation case studies regarding a DC distribution network in the PSCAD/EMTDC.