A parameter coordination method for fault current limiting impedance of flexible DC converter station based on Voltage stress analysis

DC circuit breakers (DCCB) need high operate speed and current break ability because fault current of flexible dc grid rising fast and conventional half-bridge Modular Multilevel Converters (MMC) are short of over current tolerance ability. Fault current limiter (FCL) can retrain fault current when short-circuit fault is identified, and reduce the requirement of DCCB. The equivalent circuit of MMC with FCL is proposed in this paper, and then the fault current and voltage stress of FCL with different types of fault limiting impedance are calculated; voltage stress characteristics of FCL with the change of parameters are analyzed; a parameter coordination method for different types of fault limiting impedance is proposed. The method proposed in this paper can improve fault current limiting ability of FCL without change topological structure. Works in this paper are verified through PSCAD/EMTDC simulation.