Research on flexible shutoff and blocking strategies of VSC-HVDC converter valves under AC system faults

This paper presents the research on the flexible shutoff and blocking strategies of converter valves in the VSC-HVDC transmission system under AC system faults, including global temporary blocking, phase temporary blocking, and bridge arm temporary blocking strategies of VSC-HVDC converter valves. It also analyzes the fault crossing logic and backup protection design scheme of temporary blocking strategies. The feasibility and validity verification of the phase and bridge arm temporary blocking strategies are realized through PSCAD/EMTDC and RTDS simulation. The results indicate that the blocking strategies can make the VSC-HVDC system capable of continuing the transmission of certain active power and reactive power under the AC faults, thus improving the flexible shutoff capability of converter valves under AC faults and further improving the energy utilization ratio of the VSC-HVDC system.