Frequency-Domain Reactance Based Protection for Multi-terminal DC Distribution Grid

This paper proposes a frequency-domain reactance (FDR) based protection scheme for multi-terminal DC distribution grid. First, the characteristic difference of FDR is analyzed when single pole grounding fault (SPGF) and pole to pole fault (PPF) occur respectively. Then, S-transform is used to calculate the FDR. The internal and external faults are judged by the FDR value, and the fault type is identified by the FDR ratio between the positive to negative pole. Finally, a modular multilevel converter (MMC)-based multi-terminal DC distribution grid is constructed by PSCAD/EMTDC, with extensive simulations validating the effectiveness of the proposed scheme. Simulation results show that the proposed protection method can detect the fault section rapidly and accurately.