Research On Grid Connected And Off Grid Switching Characteristics Of Energy Storage System

With the energy and environmental problems become more and more serious,new energy power generation has been widely concerned around the world,but intermittent power supply such as wind power generation also affects the power quality of the power grid.In order to improve the stability of the renewable energy power generation and improve the power quality of the power grid,the battery energy storage system has been widely used.Energy storage system is the core of the inverter,so the study of the control mechanism of the energy storage system and the various control strategies of the energy storage system under different conditions have profound theoretical and practical significance.China EPRI project will build test platform of on-grid and off-grid characteristics of energy storage.Based on this project,this paper studies the switching characteristics of grid connected and off grid of energy storage system.Firstly,the mathematical model of voltage source inverter in different coordinate system is established,the direct current control strategy of double closed loop of energy storage inverter is studied,and the different control strategies are analyzed when the energy storage system is connected to the grid and off grid.Secondly,according to the grid and off grid operation characteristics of the energy storage system in the three-phase voltage balance,the control principle of the energy storage system is analyzed,a smooth switching control strategy based on PI double closed loop control is designed,and through the simulation,the characteristics of grid connected and off grid switching are analyzed.Thirdly,in the case of unbalanced three-phase voltage,the grid connected and off grid switching control strategy of energy storage system under unbalanced grid voltage is designed.Finally,on the basis of the current inner loop control,a new method of voltage drift island detection is proposed.The detection efficiency is improved by adding a feedback voltage gain module in the current loop,and to study the success of islanding detection boundary condition of gain coefficient module in the analysis using the Hurwitz criterion;In order to prevent the inverter output power from being completely equal to the load power,the problem of the isolated island can not be detected,and the method of small fluctuation in the output power of the inverter is proposed,its effectiveness is verified by simulation.