A Novel High-Impedance Fault Recognition Method for Multi-terminal HVDC system

To enhance the protection sensitivity under high-impedance fault, non-unit protection is proposed for the multi-terminal high-voltage dc system based on the theory of variational mode decomposition and energy entropy (VMDEE). The innovation of the protection method is that the VMDEE of pole current and fault impedance are positively correlated. Therefore, the fault indicator of this protection method would increase with fault impedance, which essentially solves the problem of poor protection sensitivity under high-impedance fault. A four-terminal model of the Zhangbei HVDC grid is developed in PSCAD/EMTDC environment for case study, and the fault information is processed using the MATLAB. The reliability and efficiency of this non-unit protection are verified with simulation research considering different influence factors.