Adaptive sequential reclosing strategy for hybrid HVDC circuit breakers in MMC-based DC grids

DC circuit breaker (DCCB) is one of the most promising solutions for handling DC fault in half-bridge modular multilevel converter (MMC)-based DC grid. Generally after fault isolation, DCCBs are required to have the ability to quickly reclose so as to restore power transmission. However, the traditional simultaneous reclosing scheme may make the whole system suffer from secondary strikes such as overvoltage and overcurrent in the event of permanent faults. To solve this problem, many adaptive reclosing schemes have been proposed. Among them, the sequential reclosing scheme can achieve rapid recovery without laying any burden on the sampling and protection system. Unfortunately, secondary strikes under a reclosing failure still exist though they can be suppressed. Due to this, this paper illustrates that the overcurrent protection-based fault identification method is not able to identify the fault in time, and thus the secondary strikes are generated during the second tripping. Optimal configuration of DCCBs' parameters can reduce these adverse impacts but cannot avoid them. Based on this, an adaptive reclosing scheme is proposed. Permanent and temporary faults are recognised according to the voltage characteristics at the beginning of the fault line as soon as the arresters are conducted. Extensive simulations on a four-terminal DC grid in PSCAD/EMTDC show that the proposed method can eliminate the potential adverse impacts and is robust to fault resistance.