A Novel DCCB Reclosing Strategy for the Flexible HVDC Grid

The overhead line will be widely applied in the future flexible high-voltage dc (HVDC) grid. Correspondingly, effective reclosing strategy which can identify the fault property must be configured for the dc circuit breaker (DCCB) to improve the system power supply reliability. However, if the DCCB is reclosed directly, large second overcurrent may occur to damage the vulnerable devices in the system. Therefore, the inherent voltage characteristic difference between different dc faults (nonpermanent or permanent) is analyzed in the paper. And then a novel DCCB reclosing strategy for the flexible HVDC grid is proposed. Compared with the method which recloses DCCB directly, the proposed strategy can avoid the second damage under permanent fault condition, because it can identify the fault property without completely reclosing the DCCB (only the residual dc current breaker is reclosed before fault property identification). Moreover, compared with the typical sequential auto-reclosing strategy, the proposed strategy significantly reduces the additional control and design requirements on the DCCB. Finally, simulation cases based on the PSCAD/EMTDC are carried out to verify the correctness of the theoretical analysis and the superiorities of the proposed reclosing strategy.