A Two-Stage Protection Scheme Based on Control and Protection Coordination for AC/DC Hybrid Distribution Network

In the event of a fault in the AC/DC distribution network with modular multilevel converter (MMC), the current will surge and have a large amplitude, which seriously threatens the secure and reliable operation of the distribution network. In order to handle the fault, this paper presents an integrated control and protection strategy for AC/DC distribution network, which is based on the active current limiting control (ACLC) and single-terminal fault identification and protection principle. Firstly, an ACLC technique utilizing virtual reactance is introduced to reduce the rising rate of fault current by real-time monitoring of fault current slope. Then, taking into account the impact of ACLC, the characteristics and dynamic deviation value of single terminal current are analyzed, and a fast fault area identification method is designed. Through the cooperation of circuit breakers, this method achieves the goal of fast fault isolation. Finally, the simulation model of AC/DC distribution network is built in PSCAD/EMTDC, where the ACLC described in this paper can reduce the average rising rate of fault current by 38.4%. Moreover, the efficacy of the suggested plan is verified under different fault situations.