Research On Control Strategy Of Electric Vehicle Charging Station

With the huge consumption of fossil fuels and its resulting environmental pollutionproblems,electric vehicles have gradually replaced traditional fuel vehicles and been on the stage of the automotive industry.At the same time,as a supporting facility for electric vehicles,electric vehicle charging stations have also been rapidly developed.The combination of non-polluting,zero-emission photovoltaic power generation and electric vehicle charging stations has got a wide attention.The paper takes the optical storage type electric vehicle charging station as the research object and takes the power balance of the charging station system as the research purpose.A series of research is carried out on the photovoltaic power generation unit,the energy storage unit,the grid-connected inverter unit and the coordination control of the overall charging station system.The working principle of the photovoltaic cell is introduced,the equivalent circuit model of the photovoltaic cell is established,and the output characteristics of the photovoltaic cell are analyzed.In order to realize the maximum power tracking(MPPT)of the photovoltaic power generation system,a disturbance observation method is used to control PWM signal duty radio by applying a disturbance signal,thereby changing the switching state of the switching tube in the circuit to realize maximum power tracking.In order to carry out the charge and discharge control of the energy storage unit of the charging station system and realize the energy buffering function of the energy storage unit,set up a mathematical model of the storage battery and analyze its charge and discharge characteristics.The small-signal transfer function is deduced by the mathematical model of bidirectional DC/DC converter which is connecting the DC bus.The charging and discharging control of the energy storage unit is realized by the double-loop control method with the voltage outer loop and current inner loop.According to the grid-connected requirements of the optical storage type electric vehicle charging station,a three-phase AC/DC bidirectional converter is used as the grid connection interface of the charging station system.Then analyze its circuit topology,and the mathematical model in the d-q coordinate system is obtained through coordinate transformation.The three-phase AC/DC bidirectional converter adopts the double-loop control of voltage outer loop and inductor current inner loop,so that it can stabilize the DC side voltage quickly.And the on-off of the switching tube in the grid-connected converter is controlled bythe SVPWM modulation technology,so that energy flows in both directions between the DC microgrid and the grid.The structure of optical storage type electric vehicle charging station is designed,and four working modes of the system are analyzed.The charging station operation mode is determined according to the maximum power output of the photovoltaic system and the state of charge(SOC)of the energy storage battery.In order to solve the problem of frequent charge and discharge of energy storage cells due to bus voltage fluctuations,bus voltage hierarchical control methods are used.Finally,the effectiveness and stability of the coordinated control of the charging station system are verified through the experimental platform.