DC Grid Protection and Post-fault Restoration Scheme Using AC Circuit Breakers

Due to the lack of commercialized high voltage DC circuit breaker (DCCB), the protection of voltage source converter-based (VSC) multi-terminal HVDC (MTDC) grid is still a main obstacle hinders the development of MTDC grid. In this paper, the DC grid protection and post-fault restoration schemes using AC circuit breakers (ACCBs) are proposed. The contributions of this paper are: 1) analyses the post-fault restoration process if ACCB is used for DC grid protection; 2) analyses the difference between starting a MTDC grid from a zero-state and post-fault state; 3) DC voltage slope control is used to limit the overvoltage and overcurrent during the restart-up process. The proposed protection and restart-up control scheme will be tested in an offshore wind farm (OWF) integrated 4-terminal DC grid established in PSCAD/EMTDC. The simulation results show the effectiveness and good dynamic performance of the proposed scheme. The voltage oscillation and current surges are mitigated largely during the restart-process.