A novel pilot protection scheme for MMC-HVDC transmission lines

Overcurrent or overvoltage problems caused by DC line faults endanger the security of modular multilevel converter based high voltage direct current (MMC-HVDC) system. To improve the reliability of fault identification for MMC-HVDC transmission lines, a novel pilot protection scheme based on DC power difference is proposed in this paper. Characteristics of the DC power difference between positive pole DC power at one terminal and negative pole DC power at the other terminal are theoretically analyzed for various faults. The analysis reveals that fault detection and fault line selection can be achieved by calculating the DC power differences. According to that, the proposed protection scheme is constructed. Simulation results in real-time digital simulator (RTDS) demonstrate that the proposed protection scheme can identify and classify MMC-HVDC transmission line faults under different fault conditions accurately.