Research On Control Strategy Of Inverter Based On Virtual Synchronous Generator

With the rapid development of society,the shortage of resources and environment pollution have emerged in the world,and the micro-grid generated by renewable energy has been widely concerned and developed.The improvement of renewable energy permeability poses a threat to the stable operation of power system.Virtual synchronous generator(VSG)control technology makes the inverters simulation the inertia,damping?frequency and voltage regulation characteristics of synchronous generators,and improves the stability of micro-grid.Firstly,through analysis of the second-order mathematical model of synchronous generator,the ontology algorithm of VSG is designed according to,including the swing equation and the stator voltage equation.At the same time,through the analysis of the principle of synchronous generator governor and excitation controller,the active power-frequency controller and reactive power-voltage controller of VSG are designed.Secondly,the seamless switching technology of VSG is studied.Through the analysis of the principle of Phase Locked Loop(PLL)and pre-synchronization grid-connected based on PLL,a pre-synchronization grid-connected method without PLL is proposed.In this method,the reference axis of grid voltage in synchronous rotating coordinate system is converted to the reference axis of VSG output voltage,and then the synchronization of VSG output voltage and grid voltage can be achieved by controlling the q-axis component of grid voltage to zero,so that VSG can be connected to the grid smoothly.Then,aiming at the adverse effects of randomness and fluctuation of distributed energy on the frequency of VSG system,a cooperative adaptive control method based on moment of inertia and damping coefficients is proposed.The rotational inertia and damping coefficients of VSG are flexible and variable.By analyzing the relationship between the moment of inertia and the damping coefficient and the performance index of frequency stability of the system,an algorithm for automatically adjusting the moment of inertia and damping coefficient is designed,which can continuously adjust the transient response to suppress frequency overshoot,and at the same time speed up the frequency response,greatly improving the stability of the system operation.Finally,the simulation model of VSG is built on the MATLAB/Simulink simulation platform.The VSG islanding,grid-connected,seamless switching technology and inertia damping cooperative adaptive control strategy are simulated respectively,and the simulation results are analyzed to validate the reliability of the theory and strategy proposed in this paper.