Theoretical And Experimental Research On Smooth Transfer Control Strategy For Master-slave Microgrid

The traditional form of power generation is an important cause of environmental pollution and energy crisis.Therefore,clean and efficient distributed power generation technology has received widespread attention.Microgrids are an important way for distributed power generation to access the power grid.Microgrid has two operation modes,grid-connected and island operation.How to achieve seamless switching between the two modes is a technical problem to be solved.Microgrid has a variety of control modes such as master-slave control,peer-to-peer control and hierarchical control.This paper analyzes the master-slave control method of microgrid in detail.The master-slave microgrid has two operation modes: grid-connected and islanded.The control targets and control methods of the master source are different under different operation modes.Therefore,if the hard switching process is directly performed,problems of voltage fluctuation and current shock will inevitably be caused.Through simulation modeling of the master-slave microgrid,the hard switching process under different operating modes is simulated,and then a series of control schemes are proposed for the problems that arise.Firstly,a phase pre-adjustment control with frequency compensation is proposed for the microgrid island-to-grid connection process,which solves the inconsistency of voltage amplitude,phase and frequency information on both sides of the grid connection point at the moment of grid connection.The state follower and the reference voltage phase follower are designed for the grid-to-island process,which solves the problem of changing the internal loop input and the d-axis orientation reference phase during the control mode switching process.In order to improve the smoothness of the off-grid process,a new type of power-voltage-current three-loop control strategy is designed to ensure seamless control mode and achieve seamless switching of operating modes.In order to verify the above strategies,all control strategies were simulated and analyzed by MATLAB / Simulink software,and then the software and hardware system of the microgrid experimental platform was constructed.An automatic power generation control experiment was carried out with the help of an experimental platform,and then an off-grid smooth switching control experiment was performed on this basis.The effectiveness of some of the proposed control strategies is verified by experiments.In summary,this paper analyzes the structure and operation mode of the master-slave microgrid,and designs a new control strategy for the switching of operating modes,which provides a new idea for smooth switching from off-grid to grid.