Output Tracking Control Of Disturbed Nonlinear Systems Based On Uncertainty And Disturbance Estimator

Disturbances and uncertainties exist widely in the actual system.The uncertainties and external disturbances of the system will affect the control performance of the system.Therefore,the problem of disturbance rejection control has always been one of the hot topics in the control field.Estimating and feed-forward compensating of the disturbances is an effective disturbance rejection control strategy,as one of the disturbance rejection control methods of this strategy,the control method based on the uncertainty and disturbance estimator(UDE)uses filter to estimate system disturbance,which is simple and effective,hence it is very suitable for practical engineering.This dissertation will take a class of electromechanical system driven by motors widely existing in industry as the application background,and adopt the UDE-based control method to study the output tracking control problem of a class of uncertain nonlinear system with matched and mismatched disturbances.The main contents of this dissertation are as follows:Firstly,through analysis,it is found that the traditional UDE-based control method can effectively restrain the matched disturbance,but it is not sensitive to the mismatched disturbance.In addition,the accuracy of the filter's estimation of disturbance will affect the performance of disturbance rejection,and the filter plays a very important role in the UDE-based control method.Therefore,the selection of filter's bandwidth and order to influence the disturbance rejection performance is analyzed through the amplitudefrequency characteristic curves,which will provide a theoretical basis for the selection of the filter in the following chapters.Secondly,a UDE-based sliding mode control method is proposed for a class of second-order uncertain nonlinear systems with matched and mismatched disturbances.The proposed controller contains two parts,the reference model and the UDE-based sliding mode controller.The reference model adopts a nominal model and the reference signal is drove to track rapidly desired signal by using a nonsingular terminal sliding mode control(NTSMC),then the controller combining UDE and PID-type sliding mode surface is designed to drive the system output track reference signal.Theoretical analysis shows that the proposed control method can make the closed-loop system bounded and effectively suppress both matched and mismatched disturbances.The effectiveness of the proposed control method is verified by simulation and experiment in the speed tracking system of permanent magnet synchronous motor.Finally,a UDE-based backstepping sliding mode control method is proposed for a class of n-order uncertain nonlinear systems with matched and mismatched disturbances.In this method,the mismatched disturbance is regarded as the matched disturbance by the backstepping method,which solves the problem that the traditional UDE-based control method is not sensitive to the mismatched disturbance.Using UDE to estimate the lumped disturbance including the first derivative of the virtual control law,the phenomenon of "differential explosion" in the traditional backstepping method could be solved.In addition,a switching term with adaptive gain is introduced to eliminate the disturbance estimation error to ensure the asymptotic stability of the closed-loop system.Finally,the effectiveness of the proposed control method is verified by simulation and experiment.