Research On Stability Of Three-phase LCL Filter Inverter Based On Delay Of Digital Control System

LCL filter has been an interest recently because of its good filtering performance.However,its resonant peak at natural frequency which will bring the system problem of stability,keeps it from being more widely used.So far,aimed at solving the stability problem of LCL filters,many damping methods including active damping,passive damping and no damping,have been developed.As a way of no damping method,in this paper,the influence of the delay of digital control on the stability of inner current loop of three-phase inverter with LCL filters is systematically discussed.Firstly,this paper presents the control method which combines the ?? reference frame and dq reference frame.And then the cause of the delay of the digital control system,and equivalent numeric values of delay according to different PWM modulation methods are researched.And then according to two different feedback methods including grid current feedback and inverter-side current feedback,the delay-dependent stability criterion,the possible causes of instability and some methods enhancing stability are presented.Finally,simulation model based on Matlab and the experiment preparation are made,the simulation and experiment results verify the theory in this paper.