Reliability Evaluation Of Flexiable DC Distribution System

With the development of power electronic technology, DC distribution system is showing its advantages in connecting to distributed generations and DC loads, enlarging the capacity of power supply and improving power quality, when compare with AC distribution system. The advantages have drawn a lot of attention of the researchers. The complicated network topologies, plenty of power electronics and high permeability distributed generations in DC distribution system, will make the reliability evaluation method of traditional AC distribution system no longer suitable. Thus, in order to evaluate the reliability of DC distribution, get the optimal topology of DC system, and find out the improvement direction of high reliability urban distribution system, this research focus on the reliability evaluation of mid-voltage flexible DC distribution. First of all, many reliability evaluation methods of AC distribution system and HVDC are summarized. Furthermore, The reliability models of VSC converter station, DC/DC transformer and DC circuit breaker are established, while the effect of distributed generations on DC system are analyzed. Moreover, DC loads, back-up power, and single pole operation are all taken into consideration, together with modified minimum-cut method for DC distribution system. In addition, the reliability of three typical topologies, which contains radial topology, looped topology and two-terminal topology are compared and the best one is chosen. Finally, the reliability of AC distribution network and that of DC distribution network under existing technical conditions are compared. The key factor limiting the reliability of DC system is analyzed, and the suggestion of DC distribution is proposed.