Research On The Control Strategy Of Vsc-mtdc Distribution Network

With the increasing electricity demand and higher power quality requirement,as well as the development of green energy and electric vehicle industry,the original AC distribution network can hardly adapt to the new needs.DC distribution network is composed by distributed energy resources such as wind power,solar energy and energy storage,AC and DC loads,microgrids and converters.It is equipped with bidirectional controllbility,high reliability,power quality and flexiblity.Conventional AC distribution network is composed of transformer and transmission line,which is almost uncontrollable.However,the DC distribution network is a complex and controllable network consisting of controllable sources,controllable or uncontrollable loads,cables or overhead lines.Its key equipment is full-controlled semiconductor device(eg.IGBT).With the control and protection system,it can realize the coordination between multiple terminals and sources,which can overcome the shortcomings of AC distribution network to achieve superior performance.Research on the VSC-MTDC distribution network around the world is still under theoretical validation and lack of relevant demonstration projects.Therefore,it is of significance to conduct the study of the VSC-MTDC distribution networks as it can promote the application and development of VSC-MTDC technology.Based on the topology of the DC distribution network,this paper proposes the coordination control strategy which is based on a combination of the "instinct" operation of converters and unified management of the entire network.Moreover,a control architecture which can realize multi voltage levels is proposed.Under the constraints of voltage fluctuations,the DC distribution network is kept under stable operation.Also,a novel modeling method is proposed.On that basis,an eight-terminal VSC-MTDC distribution network is modeled.In this way,it helps to avoid the elaborate modeling of electronics.The electrical characteristics of the distribution network are perfectly remained while greatly reducing the computational complexility of computer simulation tools.It will make sense especially when dealing with the simulation of large-scale DC distribution network.