Research On Off-grid Control Technology Of Microgrid Based On Multi-battery Energy Storage System

Energy storage system is an important part of the micro-grid,which can be used in the cutting peak and filling valley of the load,improving power quality,enhancing the stability of the renewable energy power supply and preparing for the backup power,etc.Especially in the case that the superrior power supply network fails and micro-grid becomes an island,the energy storage system as a backup power restores the power supply for the load.Energy storage system needs to research the grid-conncted and off-grid control strategy to achieve these key characteristics,and as the load increases,it is necessary to find the reasonable methods to expand the capacity of energy storage system.This paper mainly discussed the control strategy of the battery energy storage system(BESS)in parallel without internet telecommunication to make sure that the micro-grid during island can be stable in operation.A method based on the droop contol was presented to implement the resonable power distribution in proportion,then the effect of closed loop parameters on the droop control strategy was researched deeply,and the droop coefficient with lead impedance was selected.The simulation under Matlab/Simulink verified the effectiveness of the proposed method.In order to realize the current-sharing control in case of the line impedance difference,virtual impedance compensation was introduced.Then Secondary frequency modulation was proposed to restore the frequency quality when the frequency is out of the range during the grid-off runtime.Then the principle of synchronous generation was analyzed and the VSG control for BESS was designed to overcome the droop control defect.The influence of the parameter of VSG on the control and the small distribution analysis was also studied,and the stability of the VSG for BESS was verified and at the same time the stability tendency as the conrol parameter changes was found.For the response speed problem of the VSG control on BESS in parallel,a self-tuning inertia parameter control was presented,which was verified by the simulation.At last the grid-off BESS experiment in parallel was made based on the hardware in loop platform due to its easy operation,security etc.The experiment on the platform verified the validity and feasibility of the control hardware circuit of BESS,and tested the effectiveness of the proposed control methods further.