Research On Anti-windup Strategy Of Repetitive Controller Of Three-phase Four-Leg Grid-Tied Inverter

With the development of new energy grid-connected technologies of wind energy,solar energy,fuel cells and so on,grid-connected inverter control strategy which plays an important role has drawn more and more attention.The repetitive controller has an integral effect on the periodic signal,so it is widely applied in the control of grid-connected inverter.However,due to the switching characteristics of the power transistor and the constraints of the DC voltage,the system maybe saturates when the repetitive controller is used,which seriously affects the quality of the power supply.This paper aims at this problem,and takes the three-phase four-leg grid-connected inverter as the object to study anti-windup strategies of repetitive controllers.The main contents are as follows:The three-phase four-leg grid-connected inverter system scheme with repetitive controllers was designed.The state-space average method is used to establish the mathematical model of the three-phase four-leg grid-connected inverter in the abc and dq0 coordinate systems.The decoupling control method in the dq0 coordinate system is designed.After the design of phase lock loop and three-dimensional space vector pulse width modulation,the overall system control scheme is established.Finally,the current repetitive controller in the abc coordinate system is designed and simulation results show the superiority of the controller.The Internal Model Cancellation Anti-Windup strategy of repetitive controllers was proposed.In order to solve the problem of unbounded growth of control quantity during saturation,this paper decomposes the expression of repetitive controller into the internal model part and the other part through factorization,and adds a compensator to the system to cancel the dynamics of internal model.When saturation,the control quantity is not integrating any more due to the cancellation of dynamics of internal model.The stability of the system is analyzed and the parameters of compensator are optimized.The simulations verify the effectiveness of the method.The Model Recovery Anti-Windup strategy of repetitive controllers was proposed.In the compensator of this method,the deviation of control quantity before saturation and after saturation is the input signal,and the two output quantities compensate the control quantity and the feedback output quantity respectively.Saturation deviation is introduced in the design of compensation of control quantity,and the linear quadratic optimal control method is used to optimize the parameters of compensator.The design of compensation of feedback output quantity introduces mathematical model of the controlled object.The simulations verify the effectiveness of the method.Finally,the analysis and comparison between this method and the internal model cancellation anti-windup strategy is made.The experimental platform of three-phase four-leg grid-connected inverter was set up to conduct experiments about the control method proposed in this paper.Based on the designs of system hardware and software,the physical platform is set up to study the performance of the controller with anti-windup function when the system is unsaturated and saturated.The results show that the repetitive controller can achieve accurate tracking of the AC signal,and the Model Recovery Anti-Windup strategy can effectively suppress the unbounded growth of the control quantity at the steady state saturation and solve the overshoot problem of current caused by the unbounded integral of the control quantity after switching of the value of current.