The improved fault location method based on natural frequency in MMC-HVDC grid by combining FFT and MUSIC algorithms

The fast and accurate fault location is extremely important for effective fault clearance in the power system. And in HVDC grid, the natural-frequency based fault location method is quite promising. Therefore, in this paper, the applicability of the traditional natural-frequency based method in MMC-HVDC grid is analyzed. Then the improved method suitable for MMC-HVDC grid is proposed. In the proposed method, the second natural frequency is discriminated and extracted to calculate the fault distance, because the first natural frequency is very low and used data window is very short in MMC-HVDC grid. In addition, the scheme combinedly utilizing FFT and MUSIC algorithms is designed, to avoid influence of traditional MUSIC false frequency phenomenon. A four terminal meshed dc grid model is built based on PSCAD/EMTDC, and the simulation cases are carried out to verify the correctness of theoretical analysis and superiorities of proposed method. Compared with traditional method, the proposed one calculates fault distance based on a shorter data window, thus being more suitable for MMC-HVDC grid. And the influence of the MUSIC false frequency phenomenon is avoided, further guaranteeing the fault location accuracy.