The Research On Micro-grid Operational Control Strategy Of Battery Energy Storage In Electric Vehicle Charging Station

Along with extensive use of electric cars,electric vehicle(EV)charging station,as the source of energy supply,develops rapidly in the same time.In order to relieve valley-to-peak in urban distribution network,EV charging station needs to be implemented to avoids bringing more serious load fluctuations;at the same time,in order to peak on the distribution network?control flow efficient?reduce loss and relieve capacity of pressure,distributed energy storage station needs to build.Therefore,if the distributed EV charging station plays a role not only in supplying electric vehicle battery,but also as a contingency reserve power,the investment costs of energy storage will reduce significantly and the urban land resources will be saved.Each individual EV charging is equal to a small power grid:it can operate in grid-connected mode,and also supply power to EV independently.So such a controlled system is called microgrid.As an effective supplement to the grid and an effective utilization form of distributed energy,the development of microgrid has changed the single power supply pattern and has greatly improved power supply reliability and efficiency.Core work is concentrated in these areas:(1)This paper combines control demand of the microgrid and characteristics of DG,studies on microgrid control methods such as master-slave control?equivalent control and hierarchical control,illustrates the principle and right conditions of constant power control(PQ control)?droop control?pour droop control?constant voltage constant frequency control(V/f control).(2)When power station is in islanded operation,the inverter output voltage amplitude and frequency fluctuating follows unstable loads.For maintaining the stability of voltage and frequency,an improved dynamic self-adjusting droop control strategy is proposed on the basis of the traditional.The method constantly revises P-E&Q-f curve locations,maintains the fluctuations of voltage amplitude and frequency within a small threshold under abrupt load variation,and makes system stable.Under the variation characteristics of frequency,voltage and current,the traditional and improved droop control strategy are analyzed based on an islanding mode established with Matlab/Simulink.The results show that the proposed method can control the voltage and frequency more effective and faster,and definitely enhance the stability of microgrid in islanding mode.(3)When microgrid is in grid-connected mode,the grid-connected inverter is designed.The grid-connected microgrid composed by single power station is built and simulated in Matlab.The results show that inverter output power follows the reference stably,and to get a good running characteristic when PQ control strategy is adapted.When multiple microgrids composed by multiple power stations are parallel operation,Distributed Generations(DG)use droop control method and PQ control method respectively.The correctness and validity of these control strategies are verified by converting DGs in the island model or grid-connected mode:for microgrid which output power is stable,droop control method is a better choice;for microgrid which easily influenced by external conditions,PQ control method is more fitness.