Research On Control Strategy Of Microgrid Off/Grid-connected Switching

In order to realize the development and utilization of new energy sources,scholars have proposed the concept of micro-grid.The micro-grid can be operated on the grid and can be operated on an isolated island.It is the key to ensure the safe and stable operation of the micro-grid.Based on the structure of optical storage microgrid,this paper conducts an indepth study on the control strategy of smooth switching of microgrid.Firstly,the two operating modes of the microgrid are introduced.The three control modes of the microgrid are analyzed from the system level.The mathematical model of the inverter is established and three basic inverter control strategies are studied: PQ control,v /f control and droop control,and designed their control structure;analysis of phase-locked loop and island detection technology principle,the control method of phase-locked loop and island conversion and the load-cut control method are given.Secondly,the in-depth study of the master-slave structure microgrid is carried out,and the temporary out-of-control problem of the micro-grid operation mode switching in the master-slave control structure is analyzed.In view of this problem,combined with the characteristics of the master-slave control which is conducive to system stability and easy to switch the peer-to-peer control,The integrated control strategy combining master-slave control and peer-to-peer control.When the method is connected to the grid,the main inverter adopts droop control.The off-grid instantaneous droop control can adjust the system voltage and frequency to realize the smooth switching of the micro grid mode and design.The control structure of the main inverter sagging outer ring and the voltage and current double closed loop is combined to analyze the off-grid process,and the pre-synchronization control method is given.Finally,the simulation structure based on optical storage microgrid is built on Matlab/Simulink simulation platform,including PQ control module,v/f control module and phase-locked loop module.The microgrid off-grid grid-connected simulation was carried out for the power supply of the grid and the power absorbed by the grid.The load-shedding control simulation was performed under the island operation.The simulation results proved the effectiveness of the integrated control strategy and load-shedding control.The masterslave control strategy under the condition is simulated,which further proves the superiority of the integrated control.