Medium and low voltage DC distribution has a good prospect of application. The transient characteristics analysis during line faults is of great significance for the design of relay protection system and the setting of protection device parameters. Two pivotal types of converters, MMC-based DC/AC converter and DAB-based bidirectional DC/DC converter, are studied under the condition of pole to pole short fault and grounding fault in bipolar DC distribution network. The equivalent circuit of these converters in different stages are then obtained and the fault voltage and current characteristics are theoretically analyzed. The impact of the position of faults, transition resistance and current limiting inductor are discussed in detail. The simulation model of DC distribution network is built based on PSCAD platform, which verifies the correctness of theoretical analysis.

DC distribution, pole to pole short fault, grounding fault, DC/AC converter, DC/DC converter