基于转移支路逐组导通的混合式直流断路器软合闸策略

Soft-Closing Strategy of Hybrid DC Circuit Breakers Based on Transfer Branch Group-by-Group Conduction

直流断路器是构建直流电网的关键设备,通过合闸实现输电线路和换流站接入直流电网、重合闸实现故障输电线路的快速恢复。本文以混合式直流断路器为研究对象,首先介绍了其合闸/重合闸工作原理,然后提出了利用转移支路电力电子模块逐组导通的软合闸策略,并分析了软合闸策略的2类基本暂态过程。通过不同合闸/重合闸应用场合下的暂态过程分析得出,直流断路器采用软合闸策略不仅可以消除输电线路接入直流电网和重合闸快速恢复故障线路时的操作过电压,而且可以实现换流站从直流侧无预充电回路并网启动。此外,还提出了软合闸过流保护方法和耗能支路能量均衡方法来优化软合闸策略,可有效减小合闸于故障的开断电流以及耗能支路能量的不平衡。最后通过PSCAD/EMTDC仿真验证了软合闸策略、软合闸过流保护方法和耗能支路能量均衡方法的正确性与有效性。

DC circuit breaker is the key equipment to construct DC power grid,transmission line and converter station can be connnected to DC power grid by closing DC circuit breaker,and the temporary fault of the transmission line can also be recovered by the reclosing operation of DC circuit breaker.In this paper,the hybrid DC circuit breaker is taken as the research object.Firstly,the closing/reclosing principles of hybrid DC circuit breakers are introduced.Then,soft-closing strategy of hybrid DC circuit breakers based on transfer branch group-by-group conduction is proposed,and two kinds of basic transient process of soft-closing strategy are analyzed.Through the analysis on the transient processes of different closing/reclosing applications,it is concluded that the proposed soft-closing strategy can reduce the overvoltage during closing/reclosing operation and realize the converter station starting from the DC side without any pre-change circuit.In addition,a soft-closing overcurrent protection method and energy balance method of energy dissipation branch are proposed to improve the soft-closing strategy,which can effectively reduce the breaking current when closing to fault and the energy imbalance of the energy dissipation branch.Finally,the validity and feasibility of the presented soft-closing strategy,and the soft-closing overcurrent protection scheme and energy balance metho are verified through PSCAD/EMTDC simulation analysis.