Identification method of MMC-HVDC converter transformers excitation inrush current and fault current based on continuous window Hausdorff distance

A single-phase ground fault on the valve side in modular multilevel converter high-voltage direct-current (MMC-HVDC) may cause commutation faults that can lead to commutation inrush current. The traditional second harmonic braking differential protection method will be invalid at this time. In order to solve the above problems, this paper proposes a new criterion for recognizing the excitation inrush current and fault current of MMC-HVDC converter based on the Hausdorff distance of continuous window, first convert the delta side current to the star side in which and then eliminate the zerosequence current from the original star side current, and then use it as the elements of sets A and B for Hausdorff distance calculation. When the Hausdorff distance is below a certain threshold for 1.5 milliseconds, the excitation inrush current due to out-of-area faults is happened. Otherwise, it is judged as the fault current due to faults in the area. Finally, the validity of the proposed criterion is verified by simulation based on PSCAD/EMTDC.