Enhanced Current Differential Protection for HVDC Grid Based on Bergeron Model: A Parameter Error Tolerable Solution

Benefiting to the immunization of distributed capacitance, Bergeron model based current differential protection has become a promising backup protection in HVDC grid. However, its performance strongly relies on the precise transmission line parameter, whereas the error of parameter is inevitable due to the frequency-dependent nature. To solve this problem, an enhanced current differential protection with parameter error tolerability is proposed in this paper. The influence of transmission line parameter error on the compensated current is investigated, where the parameter error is embodied by the characteristic impedance and velocity of traveling wave. It is discovered that the major influence comes from the error of traveling wave velocity. The main idea behind the proposed protection is to mitigate the influence from the perspective of velocity. Wavelet transform modulus maxima (WTMM) is adopted to locate and calibrate the arrival time of traveling wave. The differential current under external fault is reduced effectively, which could have been higher than that of the internal fault when the parameter error exists, and thus avoiding the protection misoperation. Finally, the feasibility and robustness of the proposed protection are validated in a four-terminal VSC-HVDC grid.