Disturbance Rejection And Anti-windup Control Design For Sampled Systems With Time Delay

Time delay is a common phenomenon existing in industrial manufacturing processes,such as energy transfer,mass transportation,and signal communication,etc.If the control design does not deal with time delay,it will seriously affect the control performance of the closedloop system,or even lead to system instability.Besides,practical manufacturing processes are inevitably subject to load disturbance.How to effectively attenuate or eliminate load disturbance is an important issue to improve system control performance.In addition,in practical control system operation,there often exists actuator saturation that could notably affect the control performance,and improper handling may even provoke instability of the closed-loop control system.Although the control methods of disturbance rejection and actuator saturation for time delay systems have been reported in the existing references,there still exist many problems to be solved,such as robust disturbance rejection and nonlinear control design,etc.This dissertation is concerned with control design methods of disturbance rejection and anti-windup design based on output measurement for sampled systems with input or output delay.The main content and contributions include:A delay-free output prediction based control scheme is proposed for non-minimum phase(NMP)systems,which could improve system performance of set-point tracking and disturbance rejection.Firstly,by using a generalized predictor to estimate the delay-free system output,a model-based extended state observer(ESO)is designed to simultaneously estimate the system state and disturbance.Then an active disturbance rejection control design is developed which consists of state feedback control and feedforward control.By configuring the transfer function poles of ESO and the desired characteristic roots of the closed-loop system,the ESO and feedback controllers are analytically derived,respectively.Meanwhile,to improve the system set-point tracking performance,a pre-filter is designed based on a desired closed-loop transfer function for the set-point tracking,such that a fast set-point tracking response without overshoot can be realized.For the presence of time-varying system uncertainties,a sufficient condition in terms of linear matrix inequalities(LMIs)is established guarantee robust stability of the closed-loop system.For sampled systems with input delay and actuator saturation,a novel anti-windup design of active disturbance rejection control(ADRC)is proposed.Based on the delay-free system output prediction,a modified extended state observer(MESO)is designed to simultaneously estimate the system state and disturbance,which could become an anti-windup compensator when the input saturation occurs.By configuring the desired poles of the closed-loop control structure for disturbance rejection,a feedback controller is analytically designed for disturbance rejection.Besides,by proposing the desired closed-loop transfer function for the set-point tracking,a setpoint filter is designed to tune the tracking performance while guaranteeing no steady-state output tracking error.For the presence of the input delay variation in practice a sufficient condition is established for guaranteeing the closed-loop system robust stability.To deal with the implemental constraint of asymmetric actuator saturation as often encountered in engineering practice,a novel anti-windup active disturbance rejection control design is proposed for sampled systems with output delay.Firstly,the asymmetric actuator saturation is transformed into a symmetric constraint.Then an anti-windup extended state observer(AESO)is designed to simultaneously estimate the system state and disturbance,which could offer antiwindup compensation when the actuator saturation occurs.To cope with time delay in the output response,a generalized predictor is adopted to estimate the delay-free output response.Correspondingly,a pole placement approach is given used to design the controller of the delay-free closed-loop system.To realize fast set-point tracking without overshoot,the controller is inversely designed from a desired set-point transfer function.By using a delay-dependent sector condition and a generalized free weighting matrix,a sufficient condition is established for guaranteeing asymptotic stability of the ADRC system.For nonlinear systems with input delay,a unified control method is proposed based on the U-model for system description.A unified U-model is adopted to describe different models of nonlinear systems,such as polynomial models,state-space models,nonlinear autoregressive moving average with eXogenous inputs(NARMAX)models,Hammerstein or Wiener type models.To tackle the input delay and nonlinear dynamics involved with the control system design,the classical Smith predictor is integrated into a U-model based predictive control scheme,such that a general two-degree-of-freedom(2DOF)control method is given for optimizing the setpoint tracking and disturbance rejection,respectively.Both controllers are analytically designed by proposing the desired transfer functions for the above objectives in terms of a linear system expression with the U-model.For the presence of time-varying system uncertainties,a sufficient condition is given for guaranteeing the control system robust stability.