Single-ended Protection Scheme for Multi-terminal VSC-based DC Distribution System Based on the Transient energy

Limited by the system architecture, line length and cost, the protection principle of traditional AC distribution systems and HVDC transmission systems cannot be directly applied to multi-terminal flexible DC distribution systems. This paper proposes a new method for line protection of multiterminal flexible DC distribution systems. Based on the boundary characteristics of the current limiting reactor installed on the line, the transient current energy difference between the fault in the protected area and outside the protected area is extracted to realize the fault identification. In order to avoid mal-operation of the non-faulty pole caused by overvoltage during unipolar grounding fault, the faulty current is firstly decoupled by phase-to-mode matrix and the decoupled 1 mode current parameters is used to calculate the transient energy. A fault direction criterion is constructed to avoid the impact of reverse faults on protection. The proposed scheme can identify faults quickly without communication, which can satisfy the speed, reliability and selectivity requirements of the DC distribution system. Simulation cases are carried out to verify the feasibility of the proposed scheme.