Abstract: With the development of medium voltage flexible DC distribution technology, the flexible DC distribution network based on power electronics technology has certain advantages over the AC distribution network in phase and frequency synchronization, flexibility of control, transmission line loss, etc., but still has deficiencies in the maturity and stability of technology, as well as the construction cost. For the medium voltage DC distribution network structure of Suzhou medium and low voltage DC distribution system project, a single-bus segmentation based " double-terminal ring " grid structure design scheme is adopted on the basis of comparison of the traditional ring structure and radiation structure. In order to meet the demand of active control of fault ride through and give full play to the flexible power supply modes of the improved grid structure, the design scheme of asymmetrical main station with half bridge converter station + mixed bridge converter station is proposed, and combined with the design of converter valve parameters and system grounding mode, a system simulation model is built on the PSCAD / EMTDC platform to verify the feasibility and fault handling ability of the engineering design scheme, which provides the analysis basis for the scheme design and equipment selection of the demonstration project.

Key words: DC distribution network, operation mode, grid structure, parameters design, DC fault