Research On Stability Control Of Gridconnected Inverter Based On Virtual Synchronous Generator In Weak Grid

With the depletion of fossil energy and the increasingly prominent environmental problems,new energy power generation based on solar energy and wind energy has developed rapidly.More and more distributed generation is connected to the grid through grid connected inverter,which leads to the increasing penetration of new energy in power system.High permeability system not only affects the stability of grid connected inverter,but also leads to the increasingly prominent characteristics of low inertia and weak damping,which reduces the anti disturbance ability of the system and seriously affects the stability of the system operation.This paper studies the stability of grid connected inverter from three aspects: the characteristics of digital controlled LCL grid connected inverter,the characteristics of virtual synchronous generator and the characteristics of short-circuit current under three-phase symmetrical short-circuit fault to ensure the static stability,dynamic stability and transient stability of grid connected inverter.The specific research contents are as follows:Aiming at the influence of digital delay on the stability of grid connected inverter in weak current grid,this paper uses phase lead compensator to increase the positive resistance range of virtual equivalent resistance to ensure the static stability of the system under short circuit ratio SCR=3,and optimizes the controller parameters according to the phase margin and amplitude margin;Aiming at the characteristics of low inertia and weak damping of grid connected inverter,this paper adopts virtual synchronous machine control strategy to increase inertia and damping for the system by simulating the rotor mechanical equation and stator excitation equation of synchronous generator,so as to ensure the dynamic stability of the system under the fluctuation of active power and grid frequency,and improve the anti-interference ability of the system;Aiming at the influence of three-phase short-circuit fault on the transient stability of distributed generation system,this paper analyzes the power angle characteristic curve of synchronous generator,and proposes a control strategy combining dynamic active power command regulation and dynamic voltage command regulation based on hybrid vector analysis,which effectively suppresses the short-circuit current of weak current grid system and ensures the transient stability of the system;Aiming at the influence of transient impulse current on system stability caused by three-phase shortcircuit fault,this paper introduces virtual resistance control method,which can effectively suppress the peak value of transient impulse current and ensure the transient stability of the system.Finally,the theoretical analysis is simulated in Simulink,and the three-phase LCL grid connected inverter platform is built in the laboratory for experimental verification.The experimental results verify the effectiveness and feasibility of the proposed control scheme.