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Single-Ended Current Differential Protection for Pole-to-ground Fault in MMC-HVDC System

Protection is one of the most challenging issues for the modular multilevel converter based high voltage direct current (MMC-HVDC) system. The pole-to-ground fault is a typical fault of MMC-HVDC system. This paper proposes a novel protection scheme for the pole-to-ground fault based on the single-ended differential current (SEDC), which is the difference between positive pole current and negative pole current at the same end. The characteristics of SEDC are theoretically analyzed for pole-to-ground fault, pole-to-pole fault and AC faults, and these characteristics are used to construct the protection scheme. A 200 kV MMC-HVDC simulation system is modeled in PSCAD/EMTDC to verify the performance of the proposed protection. Simulation results demonstrate that the proposed protection scheme can correctly distinguish the pole-to-ground fault from other faults and select the faulted line under different fault conditions.