Research On Some Problems Of DC Distribution Network

With the increasing demand for electricity and better power quality, as well as the rapid growth and wide application of new energy, new materials and power electronics technology, traditional AC distribution network is facing with the new distributed energy power access and the diversification of power requirements, besides a complex system architecture and a series of complex issues about system scheduling and coordinated control. Researches demonstrate that distribution system based on DC could be superior to an AC system in terms of efficiency, reliability and distribution capacity, and it coordinates the contradiction between the grid and distributed energy power, maximizing the value and benefits of distributed energy. Therefore, the flexible DC distribution system, which combines stability, economy, reliability and security, has a huge market potential and economic value.In this paper, a number of important issues about flexible DC distribution system will be studied and discussed. Firstly, the characteristics, advantages, network topology structure and the overall concept of DC distribution system are discussed in detail, and the network planning design, dispatching control, relay protection, key equipment and other aspects of the research situation are summarized. Secondly, the basic structure, working principle, coordinated control and scheduling policy of DC distribution system are elaborated, and the possible influence to DC distribution system caused by the renewable energy is analyzed. A simulation model of DC distribution network is built with PSCAD/EMTDC and some analysis are carried out. Then, the maximum transmission capacity, marketing price and efficiency of the major devices of AC distribution and DC distribution system are also calculated and derived, and thus, the economic analysis and comparison are conducted. For some devices, the marketing prices have to be estimated according to their development costs, because their commercial applications have not been achieved. Next, an approach based on the genetic algorithm (GA) is proposed to solve the configuration problem for the converters of DC distribution system, that is, selecting the connecting nodes of AC/DC converters when the DC system is converted from the existing AC network. In the configuration process, the total number of nodes whose voltages exceed the limits when N-1line contingency occurs is minimized, under the premise of ensuring the normal operation of the network when faults do not occur. Finally, the paper is summarized, and it points out that the DC distribution network optimization dispatching, fault diagnosis and location, etc. are the problems to study.