Research On The Control Strategy Of DC Micro-grid Based On Electric Vehicle Charging And Battery Swapping Station

Electric vehicles and renewable energy generation technology (distributed generation) are two important ways to solve the energy crisis and environmental issues. DC micro-grid is a particular distributed network with distributed generation and local load, compared with AC power distribution network DC micro-grid has the advantages of higher reliability, less line loss, excellent power quality and it is more suitable for the access of electric vehicles and distributed generations. Thus, the paper propose to build a DC micro-grid based on electric vehicle charging and battery swapping station, in order to realize the integration application of electric vehicles and renewable energy, and to achieve synergistic effects.In this paper, the DC micro-grid based on electric vehicle charging and battery swapping station is the study object, its topological structure and coordinated control strategy is mainly studied. Firstly, the problems of electric vehicle development and the existing AC power distribution network is analysed, the advantages of DC micro-grid in solving these issues are analysed, and then the concept of DC micro-grid based on electric vehicle charging and battery swapping station is proposed. Next, the topology structure, the voltage level and the major units of DC micro-grid based on electric vehicle charging and battery swapping station is analysed and designed. A power supply network with two ends is applied in proposed system, the DC bus is double bus structure with two different voltage levels. The main components of the proposed system includes load of charging station, energy storage system, grid-connected power converters and photovoltaic power generation system, the paper analyzed the operating characteristics of each component and the corresponding power electronic interface circuits are designed, the mathematical models are presented, these research are the theoretical basis of simulation model. On this basis, the multilayer control strategy of designed system is proposed, the control strategy is divided into three layers:the upper layer is the distribution network level control, which is responsible for developing the operating mode of micro-grid; the middle layer is the micro-grid level control, which is responsible for developing control objectives of micro-grid operation and the main power supply; the lower layer is of the device level control, which is responsible for the controlling of PV power adjustment and load switching and so on. In addition, the detail control processes of grid-connected opertion mode and isolated operation mode are also presented in the paper. Finally, the simulation software of PSCAD/EMTDC is used to built simulation models and two simulation examples are designed to verify the effectiveness of proposed system through and its control strategy.