Robust Repetitive Control and Disturbance Rejection Based on Two‐Dimensional Model and Equivalent‐Input‐Disturbance Approach

A new configuration of a modified repetitive‐control system has been devised for a class of strictly proper plants that suppresses exogenous disturbances and uncertainties in the dynamics of the plant. It extends the applicability of the control system. The system consists of four parts: a two‐dimensional augmented model of the plant, which takes into account the difference in characteristics between continuous control and discrete learning in repetitive control; an equivalent‐input‐disturbance estimator; a state observer; and a state‐feedback controller. A robust‐stability condition expressed in terms of a linear matrix equality is used to determine the gains of the observer and the controller. Finally, a comparison of our method with repetitive control based on linear active disturbance rejection control (LADRC) shows how effective our method is and that it is superior to LADRC‐based repetitive control.     

Robust disturbance rejection for repetitive control systems with time‐varying nonlinearities

This paper presents a disturbance‐rejection method for a modified repetitive control system with a nonlinearity. Taking advantage of stable inversion, an improved equivalent‐input‐disturbance (EID) estimator that is more relaxed for system design is developed to estimate and cancel out the influence of the disturbance and nonlinearity in the low‐frequency domain. The high‐frequency influence is filtered owning to the low‐pass nature of the linear part of the closed‐loop system. To avoid the restrictive commutative condition and choose a Lyapunov function of a more general form, a new design algorithm, which takes into account the relation between the feedback control gains and the observer and improved EID estimator gains, is developed for the nonlinear system. Furthermore, comparisons with the generalized extended‐state observer (GESO) and conventional EID methods are conducted. A clear relation between the developed estimator and the GESO is also clarified. Finally, simulations show the effectiveness and the advantage of the developed method.     

A less conservative stability criterion for sampled‐data system via a fractional‐delayed state and its state‐space model

This paper introduces a state‐space model based on a fractional‐delayed state for a sampled‐data system described as a linear system under aperiodic sampling intervals. The new state‐space model exploits the information on the sampled‐data system and the fractional‐delayed state, which is defined on the sampling interval. The fractional‐delayed state and its state‐space model are utilized to construct the Lyapunov functional, which consists of the traditional Lyapunov function and a looped functional whose boundary conditions are zeros at sampling instants. Based on the Lyapunov functional, a stability criterion and a robust stability criterion are derived in terms of linear matrix inequalities. Simulation results show the effectiveness of the proposed criterion.     

Robust disturbance rejection in modified repetitive control system

This study concerns disturbance rejection for a modified repetitive control system (MRCS) that contains a strictly proper plant with time-varying uncertainties. Since an MRCS is affected by both periodic and aperiodic disturbances, and since the disturbances are often unknown, an equivalent-input-disturbance (EID)-based estimator was added to an MRCS to yield an EID-based MRCS that compensates for all types of disturbances. In this system, the repetitive controller ensures tracking of a periodic reference input, and the incorporation of an EID estimate into the control input enables rejection of unknown periodic and aperiodic disturbances. A robust stability condition for the MRCS was established in the form of a linear matrix inequality, and the condition was used to design the parameters of the controller. This design method handles uncertainties and enables the preferential adjustment of the tracking and control performance of the MRCS. Simulation results demonstrate the validity of the method.     

基于等价输入干扰补偿的改进型重复控制系统参数优化设计

针对一类同时具有周期性参考输入和非周期扰动的伺服系统,提出基于等价输入干扰补偿的改进型重复控制系统参数优化设计方法,实现对非周期扰动的有效抑制和周期性参考输入的高精度跟踪控制.首先,利用全维状态观测器的估计误差构造等价输入干扰估计器,通过将等价输入干扰估计值反馈到控制输入端,建立基于等价输入干扰补偿的复合重复控制规律.然后,基于小增益定理推导出系统的稳定性条件,引入一个对系统抗扰性能、跟踪性能和收敛速度进行整体评价的性能目标函数,建立系统参数优化模型,采用粒子群优化算法,实现对系统重复控制器参数、等价输入干扰估计器参数和状态反馈控制器参数的同时优化.最后,通过数值仿真分析对比说明所提方法的有效性和优越性.     

具有状态观测器的鲁棒重复控制系统设计

针对一类时变不确定系统,研究基于状态观测器的鲁棒重复控制系统设计问题.通过状态观测器重构系统状态,利用重构状态进行状态反馈.基丁2维系统稳定性理论,应川线性矩阵不等式(LMI)方法,推导出了重复控制系统存在状态观测器和重复控制器的一个LMI条件,并用LMI的町行解给出了状态观测器和重复控制器参数的具体形式.最后用数值仿真验证了本文所提方法的有效性.     

Predictor‐based repetitive learning control for a class of remote control nonlinear systems

In this paper, a repetitive learning control (RLC) approach is proposed for a class of remote control nonlinear systems satisfying the global Lipschitz condition. The proposed approach is to deal with the remote tracking control problem when the environment is periodic or repeatable over infinite time domain. Since there exist time delays in the two transmission channels: from the controller to the actuator and from the sensor to the controller, tracking a desired trajectory through a remote controller is not an easy task. In order to solve the problem caused by time delays, a predictor is designed on the controller side to predict the future state of the nonlinear system based on the delayed measurements from the sensor. The convergence of the estimation error of the predictor is ensured. The gain design of the predictor applies linear matrix inequality (LMI) techniques developed by Lyapunov Kravoskii method for time delay systems. The RLC law is constructed based on the feedback error from the predicted state. The overall tracking error tends to zero asymptotically over iterations. The proof of the stability is based on a constructed Lyapunov function related to the Lyapunov Kravoskii functional used for the proof of the predictor's convergence. By well incorporating the predictor and the RLC controller, the system state tracks the desired trajectory independent of the influence of time delays. A numerical simulation example is shown to verify the effectiveness of the proposed approach. Copyright © 2007 John Wiley & Sons, Ltd.     

Design of Robust Discrete‐Time Observer‐Based Repetitive‐Control System

This paper concerns the design of a robust discrete‐time observer‐based repetitive‐control system for a class of linear plants with periodic uncertainties. A discrete two‐dimensional model is built that partially uncouples the control and learning actions of a repetitive‐control system, enabling their preferential adjustment. The combination of a singular‐value decomposition of the output matrix and Lyapunov stability theory is used to derive a linear‐matrix‐inequality‐based design algorithm that determines the control and state‐observer gains. A numerical example illustrates the main advantage of the method: easy, preferential adjustment of control and learning by means of two tuning parameters in an linear‐matrix‐inequality‐based condition.     

Model predictive control for constrained systems with uncertain state‐delays

This paper presents a model predictive control (MPC) algorithm for a class of constrained linear systems with uncertain state‐delays. Based on a novel artificial Lyapunov function, a new stabilizing condition dependent of the upper bound of uncertain state‐delays is presented in an LMI (linear matrix inequality) form. The proposed MPC algorithm is developed by following the fashion of stability‐enforced scheme. The new algorithm is then extended to linear time varying (LTV) systems with multiple uncertain state‐delays. Numerical examples illustrate the effectiveness of the new algorithm. Copyright © 2004 John Wiley & Sons, Ltd.     

Position‐dependent disturbance rejection using spatial‐based adaptive feedback linearization repetitive control

In this paper, we propose a new design of spatial‐based repetitive control for a class of rotary motion systems operating at variable speeds. The open‐loop system in spatial domain is obtained by reformulating a nonlinear time‐invariant system with respect to angular displacement. A two‐degree‐of‐freedom control structure (comprising two control modules) is then proposed to robustly stabilize the open‐loop system and improve the tracking performance. The first control module applies adaptive feedback linearization with projected parametric update and concentrates on robust stabilization of the closed‐loop system. The second control module introduces a spatial‐based repetitive controller cascaded with a loop‐shaping filter, which not only further reduces the tracking error, but also improves parametric adaptation. The overall control system is robust to model uncertainties of the system and capable of rejecting position‐dependent disturbances under varying process speeds. Stability proof for the overall system is given. A design example with simulation is provided to demonstrate the applicability of the proposed design. Copyright © 2008 John Wiley & Sons, Ltd.     

时变周期系统鲁棒重复控制设计

针对一类具有周期不确定性的线性系统,提出基于二维模型的鲁棒改进型重复控制系统设计方法.在改进型重复控制系统中,低通滤波器的嵌入将控制和学习耦合在一起.通过运用“连续提升”方法,建立连续-离散二维模型,获得能够分别优先调节控制和学习的二维反馈控制律.运用 Lyapunov 稳定性理论,推导出系统鲁棒稳定的线性矩阵不等式(LMI)条件,包含在 LMI 中的两个可调参数可以实现对控制和学习的分别优先调节.数值仿真实例验证了所提出方法的有效性.     

Design of a robust output-feedback-based modified repetitive-control system

This paper concerns the problem of designing a robust output-feedback-based modified repetitive-control system for a class of strictly proper plants with periodic uncertainties. Exploiting the periodicity of repetitive control, a continuous-discrete two-dimensional (2D) model is built so that the control and learning actions can be adjusted preferentially by means of the control gains. The combination of the singular-value decomposition of the output matrix and the Lyapunov stability theory is used to derive a linear-matrix-inequality-(LMI-) based asymptotic stability condition. Two tuning parameters in the LMI regulate the choice of the parameters in the 2D control law and thereby enable the preferential adjustment of control and learning. A numerical example illustrates the tuning procedure and demonstrates the validity of the method.     

轧辊偏心的H∞输出反馈鲁棒重复控制

针对轧辊偏心问题,用线性矩阵不等式(LMI)方法设计了用于轧辊偏心补偿控制的H∞输出反馈鲁棒重复控制器,首先引入动态输出反馈来保证闭环系统的鲁棒稳定性,把重复控制器设计问题转化为H∞动态反馈控制器的设计问题,采用变量替换法将非线性矩阵不等式转化为线性矩阵不等式并对其求解进而得到控制器参数.另外在采用上述控制器保证系统鲁棒稳定性的同时,通过在重复控制器中引入一个前向系数进一步改善和提高系统的动态性能与稳态控制精度.理论证明与仿真研究表明当系统对象参数存在摄动时,这种控制器仍能有效地补偿轧辊偏心对产品质量的影响.     

Robust delay‐dependent sliding mode control for uncertain time‐delay systems

In this paper, the problem of robust sliding mode control for a class of linear continuous time‐delay systems is studied. The parametric uncertainty considered is a modelling error type of mismatch appearing in the state. A delay‐dependent sufficient condition for the existence of linear sliding surfaces is developed in terms of linear matrix inequality, based on which the corresponding reaching motion controller is designed. A numerical example is given to show the potential of the proposed techniques. Copyright © 2007 John Wiley & Sons, Ltd.     

Design of non‐fragile guaranteed‐cost repetitive‐control system based on two‐dimensional model

This paper concerns a new method of repetitive control based on two‐dimensional (2D) system theory. First, a 2D model is presented that enables the independent adjustment of control, which happens within a repetition period, and learning, which happens between periods. Next, the problem of designing a repetitive‐control law is formulated as a state‐feedback design problem for the 2D model. An existence condition and a method of designing a robust repetitive‐control law for a plant containing time‐invariant structured uncertainties are established by combining 2D system theory with linear matrix inequalities. Then, based on those results, a non‐fragile guaranteed‐cost repetitive‐control law is derived. The controller gain to be designed is assumed to have additive gain variations. It guarantees that the value of a quadratic performance function is less than a specified upper bound for all admissible uncertainties. The main feature of this approach is that it enables the control action and the learning process to be adjusted independently by the direct tuning of the weighting matrices in the quadratic cost function. Finally, a numerical example demonstrates the validity of this approach. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Observer‐based tracking control for switched stochastic systems based on a hybrid 2‐D model

This paper is concerned with the observer‐based output tracking problem for a class of linear switched stochastic systems with time delay and disturbance by using repetitive control approach. More precisely, a two‐dimensional hybrid model is incorporated to obtain and optimize the repetitive controller. In particular, the repetitive controller is used to improve the tracking performance through its continuous learning actions. In addition, an equivalent‐input‐disturbance estimator is incorporated into the repetitive control design approach to reduce the effect of the external disturbances. The main aim of the control design is to track the periodic reference signal with the measured output of the system under consideration even in the presence of an unknown bounded disturbance. By constructing a suitable Lyapunov‐Krasovskii functional and using average dwell time approach and Jensen inequality, sufficient conditions are obtained in terms of linear matrix inequalities to guarantee the mean‐square exponential stability of the considered system. Eventually, a numerical example is provided to demonstrate the effectiveness of the developed method.     

线性不确定系统的H∞状态反馈鲁棒重复控制

现有的重复控制设计不能同时优化低通滤波器的参数和重复控制器的参数.我们在设计重复控制系统以控制线性不确定对象时,解决了这个问题.首先,引入状态反馈以保证闭系统的鲁棒稳定性,把重复控制器设计问题转化为H∞状态反馈增益的设计问题.为获得低通滤波器最大转折频率,进一步将设计问题转化为基于线性矩阵不等式约束的凸优化问题.提出了一种迭代算法,用以计算低通滤波器的最大转折频率和H∞状态反馈增益.在保证系统鲁棒稳定性的同时,获得最高控制精度的重复控制器和低通滤波器的参数组合.该方法与已有方法比较,它的结果容易验证和求解,因而更适合于实际应用.最后,通过数值实例验证了本文所提方法的有效性.     

Robust control for uncertain nonlinear systems with state‐dependent control direction

The control direction is the multiplier of the control term. In this study, the control direction is considered as an unknown function of state and allowed to cross zero and change its sign smoothly. Based on the analysis of system dynamics at the points where the control direction is zero, a robust controller is proposed by integrating with a bounding function and a Nussbaum‐type gain. Under the proposed controller, the system approaches zero if zero is accessible, or to the accessible point closest to zero if zero is not accessible by any control. The control performance is illustrated by simulated examples. Copyright © 2010 John Wiley & Sons, Ltd.     

基于二维混合模型的保成本重复控制

针对一类线性不确定系统, 提出一种基于二维混合模型的重复控制设计新方法, 研究具有反馈作用的保成本重复控制设计与优化问题. 首先, 为了提高系统稳定性, 将反馈控制器引入到重复控制系统中, 设计一种具有反馈作用的重复控制系统结构; 然后通过建立重复控制系统的连续/离散二维混合模型, 将重复控制器设计问题转化为一类连续/离散二维系统的状态反馈控制问题. 在此基础上, 对给定的线性二次型性能指标, 给出闭环系统的保成本重复控制律参数设计及其优化方法. 对所有容许的不确定性, 保成本重复控制使稳态跟踪误差渐近稳定的同时, 线性二次型性能指标值小于某个常数. 所得结果以线性矩阵不等式的形式给出, 可利用MATLAB工具箱方便地求解.最后, 数值仿真验证了本文所提方法的有效性.     

Design of discrete-time repetitive control system based on two-dimensionalmodel

This paper presents a novel design method for discrete-time repetitive control systems (RCS) based on two-dimensional (2D) discrete-time model. Firstly, the 2D model of an RCS is established by considering both the control action and the learning action in RCS. Then, through constructing a 2D state feedback controller, the design problem of the RCS is converted to the design problem of a 2D system. Then, using 2D system theory and linear matrix inequality (LMI) method, stability criterion is derived for the system without and with uncertainties, respectively. Parameters of the system can be determined by solving the LMI of the stability criterion. Finally, numerical simulations validate the effectiveness of the proposed method.