Detection Method Based on Median Mode Decomposition in Multi-terminal DC System

Several frequency-domain based fault detection methods were developed in the high voltage (HVDC) system in recent years. In this paper, a modified empirical mode decomposition (EMD) designated as median mode decomposition (MMD) is introduced, and a new fault detection method is developed based on that. Compared with the traditional EMD, MMD is able to obtain the intrinsic median mode function (IMMF) with less sifting iterations, leading to less computation burden in the actual use. This characteristic is useful for dc fault detection because the detection delay of dc fault should be limited within 3 ms. By obtaining the Hilbert spectrum of the IMMF after MMD, the fault transient is able to be differentiated within 0.35 ms detection delay with reliable discrimination. This method is verified by simulation results in a 4-bus ring multi-terminal dc (MTDC) system in PSCAD. It is also compared with other fault detection methods to test its validity.