Research On Energy Storage Capacity Configuration And On-off-grid Switching Technology Of Optical Storage Microgrid

In the development of new energy technologies in China,photovoltaic-storage microgrids are an important part of China's current microgrids.In the photovoltaic-storage microgrid,the configuration of energy storage and the smooth switching of microgrid when it is connected to and disconnected from the grid,play a vital role in maintaining the stable operation and improving the power quality.Therefore,it is of great practical significance to study the optimization of the energy storage capacity of photovoltaic-storage microgrid and the control technology of grid-connected and off-grid switching.This thesis takes the photovoltaic-storage microgrid as the research object,and focuses on the energy storage capacity configuration and grid-connected off-grid smooth switching control technology in the microgrid.Through the analysis of photovoltaic output characteristics and load composition in the photovoltaic-storage microgrid,uses an improved particle swarm algorithm to rationally allocate energy storage,then studies the grid-connected and off-grid operation control methods of the photovoltaic-storage microgrid,builds a microgrid controller based on energy storage,proposes an applicable off-grid switching control strategy,and finally verifies its function through simulation.The details are as follows:Firstly,the characteristics of photovoltaic output,load composition,and various applications of energy storage in microgrids are analyzed,and the effects of the three on energy storage capacity allocation are summarized.Based on this,a more suitable capacity allocation method is proposed.The method takes the minimum daily operation cost of the microgrid and the minimum power fluctuation in the grid as the objective function,and meets the constraints of microgrid power balance,energy storage battery charge and discharge,etc.And by adding the maximum power supply constraints and energy storage margin constraints of the distribution network,the traditional particle swarm update method is improved to more accurately configure the appropriate capacity for the photovoltaicstorage microgrid.Moreover,constant voltage charge and discharge control method,PQ control method and VF control method were studied.Based on this,the grid-connected controller and offgrid controller of the photovoltaic-storage microgrid were constructed.Then,analyze the existing problems during the switching of the photovoltaic-storage microgrid,and add the inner loop control pre-synchronization link to solve the problem of the inner loop control state being out of sync when the grid is switched to off-grid;add the grid voltage presynchronization link to solve the problem of the voltage amplitude,phase,and frequency status of the access points of the micro-grid and distribution network are not synchronized when switching from off-grid to grid.Finally,the solution is integrated to propose an offgrid dual-mode bidirectional switching control strategy.This strategy uses a presynchronization method,which uses the state before switching to synchronize the state after switching,makes the microgrid state consistent before and after the switch,thereby completing the smooth switch.Finally,MATLAB software was used to configure the energy storage capacity of the photovoltaic-storage microgrid,and a model was built in simulink for simulation verification.The simulation results show that the photovoltaic-storage microgrid with appropriate energy storage capacity and the use of the off-grid strategy proposed in this thesis can achieve stable operation and reliable power supply during grid-connected,off-grid,and two-way switching,which proves that the technology studied in this thesis can make photovoltaicstorages play a greater role.