Coordinated Protection Strategy of DC Circuit Breakers Under N-3 Fault of Flexible DC Grid

In view of the characteristics of the four-end loop network in the Zhangbei flexible DC project and the requirement that the fault of the MMC flexible DC grid needs to be cleared quickly, the protection strategy and fault isolation technology of the four-end loop network were studied. In this paper, the fault of DC circuit breaker was analyzed and compared. The fault can be quickly removed by combining DC circuit breaker with coordination control. The protection scheme of flexible DC network based on DC circuit breaker failure is proposed, and the model is built on MATLAB for simulation and verification. The simulation results show that the proposed fault protection scheme can break the adjacent DC circuit breaker correctly when the DC circuit breaker fails, so as to achieve the purpose of protecting the stable operation of the system. Among them, the main branch and transfer branch current tolerance of the fault DC circuit breaker and the normal opening and breaking DC circuit breaker meet the technical design requirements.