Micro-grid Coordinated Control With Distributed Energy Storage Of Electric Vehicles Operational Research

Restricted by factors such as the climate environment and its own conditions(volatility,randomness,uncertainty,etc.),the output of renewable energy sources such as wind power and photovoltaics has great uncertainty.Restricted by the capacity of large-scale grids,when the large-scale renewable energy being connected to the gird,the randomness and volatility will affect the stability and power flow distribution of the large-scale grid,and then affect the large-scale absorption capacity of renewable energy.‘Wind curtailment’ and ‘difficulty in grid connection are still key issues that limit the large-scale consumption of renewable energy.In order to effectively suppress the volatility problems in the process of grid connection of renewable energy,domestic and foreign experts have proposed a wind/photovoltaic storage micro-grid system.The energy storage unit can quickly realize the time and space translation of the electric energy in the micro-grid system,and smooth the Grid-connected power fluctuation of the wind/photovoltaic storage micro-grid systems.At the same time,in the case of isolated grid operation of the wind/photovoltaic storage micro-grid system,the energy storage system can be used as a voltage source to maintain the system’s active and reactive power balance,and achieve voltage and frequency stability under the isolated grid operation of the micro-grid system.With the large-scale popularization and application of new energy electric vehicles,new energy electric vehicles can be connected to the micro-grid system as an uncertain load during the charging process.The uncertainty of the charging and discharging time of electric vehicles causes the time uncertainty of being connected to the micro-grid.If a large number of new energy electric vehicles are randomly connected to the micro-grid system,it will seriously affect the safe and reliable operation of the micro-grid;At the same time,when electric vehicles are connected to the micro-grid as an auxiliary distributed energy storage method,how to participate in the dynamic and rapid adjustment of the voltage and frequency of the micro-grid system on the basis of ensuring the performance of the electric vehicle itself is of great significance for the safe and stable operation of the micro-grid system with the electric vehicle distributed energy.Therefore,the construction of a coordinated operation strategy for a micro-grid system with electric vehicles distributed energy storage for improving the structure of the micro-grid system and improving the broad adaptability of the micro-grid system has important research value.Based on the improvement of droop control and electric vehicle charging and discharging strategies,this paper conducts research on the coordinated control strategy of micro-grid with electric vehicle distributed energy storage.The related work carried out in this paper is as follows:(1)Overview and summarize the classification of micro-grid structures with electric vehicles distributed energy storage and the current research status of micro-grid control with electric vehicles distributed energy storage;Summarize the characteristics of the overall control strategy of the micro-grid system;The principle and control process of different control strategies of the source DC/AC converter are analyzed in detail;(2)Construct a typical micro-grid isolated system mathematical model with electric vehicle distributed energy storage: Among them,the renewable energy uses photovoltaic power generation system,and the energy storage unit uses an improved droop control strategy.The improved droop control strategy is based on the traditional droop control strategy by adding the voltage and frequency secondary adjustment fuzzy control link to realize the secondary rapid adjustment of the voltage and frequency of the converter.Based on simulation software,a single converter simulation model of the improved droop control strategy,and compare the output curves of the converter before and after the improved droop control strategy through simulation to verify the effectiveness of the improved droop control strategy proposed in this section;(3)Construct a DC/AC converter control strategy for the micro-grid system with electric vehicle distributed energy storage,and propose a three-layer DC/AC control strategy for electric vehicles: the bottom layer adopts traditional PQ control,the middle layer adopts virtual inertia and a frequency modulation strategy,The upper layer is based on the optimized control strategy of the charge and discharge power of electric vehicles in the state of charge;on the basis of the improved droop control strategy,the overall coordinated control strategy of the off-grid micro-grid with electric vehicle distributed energy storage is constructed.The simulation curves under two working conditions verify the effectiveness of the isolated-grid micro-grid coordinated control strategy with electric vehicle distributed energy storage proposed in this paper.Two working conditions are :The isolated-grid micro-grid system is switched on and off;the output of the renewable energy changes.