Adaptive reclosing scheme for flexible HVDC grid with single-pole ground fault based on residual voltage zero-crossing detection

To avoid the issue of blind reclosing in conventional flexible high voltage direct current (HVDC) grid, investigating an adaptive reclosing scheme capable of identifying fault nature and duration is essential. This paper proposes a single-pole ground fault adaptive reclosing scheme based on residual voltage zero-crossing detection for flexible HVDC grid equipped with hybrid DC circuit breakers (HDCCB). First, the working principle of HDCCB and the expressions of residual voltage under different fault natures are analysed. Secondly, based on the zero-crossing detection principle, the differences in zero-crossing characteristics before and after the fault are used to identify the fault nature and calculate the fault duration. Finally, a flexible HVDC grid model is developed using the real-time digital simulator (RTDS) platform to verify the proposed scheme through simulation. The results demonstrate that the adaptive reclosing scheme accurately identifies fault nature and calculates fault duration with an error margin of less than 3 ms, exhibiting significant tolerance to fault resistance.