基于主动限流控制的直流配电网保护及故障隔离方案

DC faults in flexible DC distribution network could easily lead to overcurrent, which seriously threatens the safe operation of power grid. Modular multilevel converter (MMC) blocking is mostly used to cut off the fault current in FBSM-MMC based distribution network, but the blocking will cause power outage of the whole network for a moment, which reduces the reliability of the power supply. To solve the problem, a protection and fault isolation scheme based on active current-limiting control of FBSM-MMC for flexible DC distribution network is proposed, which consists of three stages. After a short-circuit fault occurs, the output DC current of the inverter will be limited to 1.2 times of the rated current by the control of MMC (stage 1). The faulty line is identified according to the synchronous zero-crossing characteristic at both ends of each line (stage 2). A fault isolation scheme which contains the cooperation of DC circuit breakers and high-speed switches is proposed (stage 3). By disconnecting the DC breaker associated with the fault and controlling the output DC current of the corresponding converter station to be reduced to 0, the mechanical switch on the fault line can also be quickly turned off, thereby achieving fault isolation. Finally, a four-terminal flexible DC distribution network model is built in PSCAD/EMTDC, and the feasibility of the proposed protection and fault isolation scheme are verified through a large number of simulations.