Research On The Operation Characteristics Of An Independent Wind-solar Storage DC Microgrid With Fast Charging Of Electric Vehicles

Distributed photovoltaic and wind generation is one of the effective way of renewable energy utilization.Microgrid aims to realize the flexible and efficient utilization of distributed source.And with the increase of the number of new energy electric vehicles,using micro grid or micro grid group to charge electric vehicles can effectively alleviate the upgrading pressure brought by its energy demand to the large power grid.Based on the topology design of wind / photovoltaic / storage DC microgrid with electric vehicle fast charging,this paper proposes a hierarchical coordinated control strategy.The bottom control can ensure the stable operation of the system and solve the DC bus voltage instability caused by electric vehicle fast charging.On this basis,considering the actual operation conditions of the independent wind / photovoltaic / storage DC microgrid with electric vehicle fast charging,the upper central controller is designed,which can select the system operation modes and change the reference value of the local controller.This paper mainly includes the following points:(1)The mathematical models of each generation unit and energy storage unit of wind / photovoltaic / storage DC microgrid are established,and the maximum power tracking control and power limiting control of photovoltaic and wind power units are studied.By fitting the relationship between photovoltaic output power and port voltage under different light intensities,the photovoltaic power generation unit realizes maximum power tracking by looking up the table,and realizes power limiting operation by changing the port voltage.According to the relationship between wind speed and generator speed,the reference speed of the unit corresponding to the maximum output power under the wind speed is obtained.The double closed-loop control of speed outer loop and current inner loop is adopted to realize the maximum power tracking control of the wind power unit,and the power limiting operation of the unit is realized by controlling the pitch angle of the wind turbine.(2)This paper studies the load carrying capacity of the parallel energy storage system with constant power load using V-I droop control.Firstly,the constant power characteristics of electric vehicle charging load with power electronic interface are analyzed.Then,the average value model of bidirectional DC/DC converter with V-I droop control is established.The load carrying capacity of resistive load and constant power load with V-I droop controller is analyzed by using eigenvalue method and impedance analysis method,and the control method to ensure the stable operation of the system is given the parameters of the converter are stable operation boundary and system loading capacity.The developed three-phase interleaved DC/DC converter and dspace1103 are used for experimental verification.(3)Considering the actual operation conditions of the independent wind /photovoltaic / storage DC microgrid with electric vehicle fast charging,the upper central controller which can select the system operation mode and change the reference value of the lower co ntroller is designed.Firstly,the capacity and power boundary of each generation unit and the possible communication distance are analyzed,and the upper central controller is selected.According to the actual operation condition of the system,the possible operation state of the system and the switching condition between each operation state are formulated.Using Matlab /Simulink / stateflow simulation software,the main circuit model and control system of wind / photovoltaic / storage DC microgrid with electric vehicle fast charging load are built,and the system simulation under different operating states is carried out.The simulation results verify the effectiveness and feasibility of the proposed hierarchical coordinated control strategy.