Reliability Comparison of AC and DC Distribution Network

To explore the development direction of high reliable distribution network in future, it was the first time to research the reliability of medium-voltage flexible DC distribution network in depth. The reliability models of VSC converter station, DC/DC transformer and DC circuit breaker were established; considering the impacts of the DC load, the reserve power supply and distributed generation, the minimum-cut set method was improved to make it suitable for the reliability assessment of both AC and DC distribution networks. Taking loop distribution network for example, the reliability of AC distribution network and that of DC distribution network under existing technical conditions were compared. Comparison results show that at the present stage the reliability of DC distribution network is lower than that of AC distribution network; with the increase of the proportion of DC load the reliability of DC distribution network will be improved, however the effectiveness will be limited; the high failure rate of DC circuit breaker and DC/DC transformer is the very factor that restricts the reliability improvement of DC distribution network at the present stage. With the progress of power electronic elements, the reliability of DC distribution network would be close to that of AC distribution network gradually and even higher than that of AC distribution network.