Line Protection Scheme for MMC-based Multiterminal DC Distribution Grid

For flexible medium-voltage DC distribution grid, this paper proposes a DC line protection method. Frist, characteristic differences of transient current variation at both ends of the line are analyzed when fault occurs. Afterwards a line protection scheme is proposed based on initial current travelling wave. Through comparing the polarity of current modulus maxima at both ends of the line, the method can identify the internal and external faults. A modular multilevel converter (MMC)-based multi-terminal DC distribution grid is constructed using PSCAD/EMTDC, and extensive simulations are conducted to validate the effectiveness of the proposed scheme. Simulation results show that the proposed protection method can detect the fault section rapidly and accurately.