Fault current limiter for the MMC-based multi-terminal DC grids

In the modular multilevel converter (MMC)-based multi-terminal high-voltage direct current (HVDC) system, the fault current rises rapidly due to sub-module capacitors discharging when a DC-side short-circuit fault occurs, which makes the MMC easily blocked for self-protection. To avoid the blocking of the converter station and lower the DC fault current, this study proposes a novel fault current limiter (FCL) for MMC-based multi-terminal DC grids. First, the fault current limiting circuit, which consists of resistance, capacitance and power electronic components is designed. Then, the operation principle of the FCL is analysed in detail. Afterwards, the startup criterion is constructed, and the selection method of the key parameters in the fault current limiting circuit is also introduced in order to prevent the converter station from blocking in the case of DC short-circuit fault. Finally, a simulation model was built using PSCAD/EMTDC software, and extensive simulation results verified the effectiveness of the proposed FCL.