The modular multilevel converter(MMC)based high voltage direct current(HVDC)grid is an effective solution to transfer the fluctuating renewable source energies such as photovoltage(PV)and wind power

and the DC fault current limiting is one of the most important technical challenges in the line protection. This paper considers the action processes of the fault current limiter(FCL)and DC circuit breaker(DCCB)along with the energy consumption characteristics of the MOAs based on the capacitor discharging mechanism of the bipolar HVDC gird under pole-to-pole short circuit fault. Based on frequency-dependent(phase)line model

the DC fault current characteristics before and after the insertion of the inductive FCL are analyzed on PSCAD/EMTDC. In bipolar four-terminal DC grid

the simplex algorithm is used to optimize the configuration of the fault current-limiting reactors of each DC line with the following two objectives: (1)the minimum sum of the cut-off currents of the DCCB at each DC bus; (2)the minimum sum of the energy consumption of the shunt MOAs of FCLs and the MOAs of DCCBs. The current-limiting reactor optimization configurations of each DC line under various weights are given.