Finite Time Tracking Control For Disturbed Nonlinear Systems With Input Saturation

The control systems in practical engineering are inevitably affected by uncertainties and disturbances.The disturbance rejection control problem has always been a research hotspot in the control field.Finite time controller contains fractional power terms,which makes the closed-loop system with finite time control have better performance on robustness and disturbance rejection than the closed-loop system with non-finite time control.In addition,due to the limitation of physical conditions,the input saturation nonlinearity exists in many control systems,which may degrade the performance of the control system,even lead to system instability,if not processed during the control system design.Therefore,the finite-time tracking control for a class of uncertain nonlinear systems with input saturation and disturbances is studied in this dissertation.The main research contents of this dissertation are as follows:Firstly,a backstepping integral sliding mode control algorithm based on finite time extended state observer is proposed for a class of nonlinear systems with input saturation and time-varying disturbances.The hyperbolic tangent function is employed to approximate the input saturation function,and the approximation error and the uncertainties and disturbances of the system constitute the lumped perturbation.A finite time convergence extended state observer is applied to estimate the lumped perturbation,and the estimate is introduced into the controller for feedforward compensation.A compound controller combining with backstepping technique and integral sliding mode control method is then developed.In order to avoid the "differential term explosion" in the traditional backstepping method,a first-order low pass filter is introduced in each step of backstepping procedure.Theoretical analysis shows that the proposed method can ensure that the system tracking error can converge to the origin in finite time.The simulations and experiments are carried out on the permanent magnet synchronous motor speed tracking control system to verify the effectiveness of the proposed control algorithm.Secondly,considering the unknown control coefficient in nonlinear systems,an adaptive practical finite-time control algorithm is proposed.The algorithm first describes the saturation by introducing an input saturation equation;then combines the backstepping method to design an adaptive practical finite time controller,and introduces a sliding switching term in the controller to counteract the influence of disturbance on the system,and introduces a time-varying gain to reduce chattering caused by the switching signal in the controller.Theoretical analysis shows that the system tracking error can converge to the neighborhood near the origin in a finite time.Finally,a rigid spacecraft system is used as an example to simulate,and simulations and experiments are performed on the permanent magnet synchronous motor speed tracking control system to verify the effectiveness of the proposed control algorithm.Finally,an adaptive sliding mode finite-time tracking control algorithm is proposed for a class of multivariable nonlinear systems with time-varying disturbances,asymmetric input saturation and partly unknown states.The algorithm first uses a finite time state observer to estimate the unknown states of the system,and then an adaptive second order sliding mode finite time controller is designed based on the second order nonsingular fast terminal sliding mode surface,and introduces a variable gain sliding mode switching term in the controller to offset the influence of disturbance while reducing the chattering in sliding mode control;Finally,the effectiveness of the proposed control algorithm is verified by simulation on a rigid spacecraft system.