Fault Isolation Scheme based on Circuit Breaker Optimization Strategy in DC Distribution Network

The DC distribution network with full-bridge modular multilevel converter can clear the fault current by blocking the converter, then the fault can be isolated by the DC switch. However, a short-term power outage of the network occurs under this scheme and the reliability of power supply is seriously affected. Although the DC circuit breakers can isolate the fault before converters' blocking, and improve the reliability of power supply, its cost is high and the number of circuit breakers directly determines the cost of network construction. In view of this, how to determine the configuration principle of the circuit breaker and avoid short-term power outages during DC faults is the biggest challenge in current research. To solve this problem, this paper first introduces that the converters should absorb the power of the healthy distribution line after the disconnection of the circuit breaker. Then, the circuit breaker's setting principle is proposed according to the definition of the cut-set. The heavy-load line of the distribution network is taken as the reference, and the minimum cut-set can be found in the cut-set containing the heavy-load line. Then, the minimum cut-set with the least number of distribution lines is determined as the circuit breaker setting position. Under the proposed method, the minimum number of circuit breakers can be used to isolate fault and the problem of network-wide power outage caused by fault self-clearing is solved based on the active control of converters. Finally, a five-terminal DC distribution network model is established in PSCAD/EMTDC, and the robustness of different strategies are verified by simulation results.