一类多不确定性系统鲁棒H∞控制器的LMI设计方法

对同时具有加型参数不确定性以及积分二次约束(IQC,integral quadratic constraint) 不确定性环节的一类线性系统,给出设计其鲁棒H∞状态反馈控制器和动态输出反馈降阶控制 器的设计方法.在具体推导过程中,首先基于动态耗散理论,考虑了无输入情况下系统只具不 确定性闭环环节时的鲁棒H∞稳定性问题.然后基于这一条件,针对典型的无源类和有限增益 类不确定性,推出了系统同时具有多不确定性时进行鲁棒H∞状态反馈控制器和动态输出反馈降 阶控制器设计的充分条件.所有可解条件都可化为标准的LMI(1inear matrix inequality)求解.     

基于参数依赖动态输出反馈鲁棒MPC的混沌系统同步

针对离散时间不确定混沌系统的同步控制问题,提出一种基于参数依赖动态输出反馈鲁棒模型预测控制算法.首先,采用主动控制策略,将具有噪声扰动的主从混沌系统同步问题转化为鲁棒稳定性问题;然后,采用参数依赖动态输出控制器和二次有界概念,在保证闭环系统鲁棒稳定性的同时,降低算法的保守性;最后,通过附加约束条件,能够显式处理混沌系统同步中的输入约束.仿真结果表明了所提出算法的有效性.     

基于有限频段的Markov跳变系统有限时间H∞滤波

传统Markov跳变系统H∞滤波方法要求所有子系统对全频域的噪声具有同样的干扰抑制水平,由于没有充分利用噪声的频率信息,导致传统滤波方法可能含有较大的保守性.本文针对特定频段的干扰信号,提出基于有限短时间的H∞滤波器设计方法.在引入有限频段的同时,结合有限短时间稳定理论,提出有限频段以及有限时间两尺度滤波方案,为降低滤波理论的工程保守性提供了思路.仿真结果表明本文所提滤波方法与现有滤波方法相比,具有一定的优越性.     

参数不确定离散时间系统的有限时间输出反馈预见控制器设计

基于参数依赖的Lyapunov函数方法及LMI技巧,研究一类参数不确定离散时间系统的有限时间输出反馈预见控制问题.首先,采用预见控制理论中误差系统的方法,引入差分算子和离散提升技术,构造出包含未来目标值信号和干扰信号的信息的扩大误差系统,将有限时间预见控制问题转化为扩大误差系统的有限时间稳定性问题;然后,针对所推导出的扩大误差系统设计输出反馈预见控制器,通过改造输出方程以充分利用可预见信号的未来信息,并通过LMI技巧给出闭环系统有限时间稳定的条件及预见控制器的设计方法.研究结果表明,通过求解LMI,可确定静态输出反馈预见控制器增益矩阵.数值仿真表明了所提出方法的有效性.     

一类二阶非线性系统的有限时间状态反馈镇定方法

针对一类二阶非线性系统的有限时间状态反馈镇定问题进行了讨论. 给出了三种基于连续状态反馈的全局有限时间状态反馈镇定方法. 首先，利用非线性齐次系统性质，设计出一种状态反馈控制器，使得闭环系统渐近稳定并且具有负的齐次度；其次，基于有限时间Lyapunov函数的反步构造法，给出了一种有限时间控制器；最后，利用非奇异终端滑模控制技术，得到了一种使闭环系统有限时间收敛到平衡点的反馈镇定控制器. 仿真结果表明了这些方法的有效性.     

具有次优保性能滑动模态的静态输出反馈滑模控制

针对一类不确定系统,提出了一种具有次优保性能滑模面的静态输出反馈滑模控制方法.首先将滑模面的设计问题等价为一个对称矩阵的求解问题,基于等效控制法,推导了保性能滑模面存在的充分条件.然后基于迭代线性矩阵不等式(iterative linear matrix inequality,ILMI)方法,给出了次优保性能线性滑模面的求解算法,最后基于线性矩阵不等式(linearmatrix inequality,LMI)方法,设计了输出反馈滑模控制器,使得闭环系统渐近稳定且切换函数能在有限时间内到达零.该方法首次实现了输出反馈滑模面的优化,且具有保守性小、无需对被控系统模型进行坐标变换的优点.仿真结果验证了本文方法的优越性.     

时滞系统的输出反馈滑模控制的一种奇异系统方法

利用一种奇异系统方法讨论了时滞系统的输出反馈滑模控制问题. 时滞系统的非线性项满足范数有界约束.首先,将滑动模态与线性切换面作为一个奇异时滞系统,基于奇异时滞系统的稳定性理论, 给出滑动模态稳定及切换面存在的线性矩阵不等式(Linear matrix inequality, LMI)充分条件.然后,给出使得系统闭环渐近稳定的静态输出反馈滑模控制器的设计方法,此控制器保证闭环 系统有限时间到达切换面.最后,用数值算例验证本文方法的有效性和正确性.     

具有全状态约束和未建模动态的严格反馈系统有限时间自适应动态面控制

针对一类具有全状态约束、未建模动态和动态扰动的严格反馈非线性系统,通过构造非线性滤波器,并利用Young’s不等式,提出一种新的有限时间自适应动态面控制方法.引入非线性映射处理全状态约束,将有约束系统变成无约束系统,利用径向基函数逼近未知光滑函数,利用辅助系统产生的动态信号处理未建模动态.对于变换后的系统,利用改进的动态面控制和有限时间方法设计的控制器结构简单,移去现有有限时间控制中出现的“奇异性”问题,可加快系统的收敛速度.理论分析表明,闭环系统中的所有信号在有限时间内有界,全状态不违背约束条件.数值算例的仿真结果表明,所提出的自适应动态面控制方案是有效的.     

非对称约束下非线性系统的有限时间控制

针对具有非对称输出约束和外界干扰的非线性不确定系统,提出了基于固定时间干扰观测器和非对称障碍函数的有限时间控制策略。首先,采用非对称障碍函数处理系统的输出约束问题,保证输出满足约束条件;其次,通过构造固定时间干扰观测器对外界干扰进行估计,且估计误差在固定时间内收敛到零;再次,基于Lyapunov稳定性理论证明闭环系统在有限时间内有界稳定且输出满足约束条件;最后,通过永磁同步电机的仿真实验验证了所设计的控制策略的有效性。     

有限频域约束下串联弹性驱动器的刚度控制

工程实际中的被控对象都具有明显的有限频域特性,但目前的物理人机交互研究大多是针对全频域性能指标来设计阻抗控制器,由此得到的控制器往往失之保守.本文针对绳牵引串联弹性驱动下的人机物理交互问题,采用有限频域性能约束方法来提升系统在设定频段的刚度控制性能.首先,分析绳牵引串联弹性驱动的刚度控制目标并将其转化成有限频域性能约束下的H∞控制问题.其次,根据广义Kalman-Yakubovich-Popov (KYP)引理,将有限频域性能约束转化成矩阵不等式条件,进而分解变换成有关全信息控制器和待求的静态输出反馈控制器的条件.然后,求解出一个满足条件的全信息控制器,并迭代优化得到输出反馈控制器.仿真和实验结果都表明,本文方法在设定频段取得了更加精确的刚度控制效果.     

Delay-dependent state feedback control with small gain conditions in finite frequency domains

This article studies the problem of control synthesis via state feedback for linear continuous-time multi-delay systems with small gain conditions in finite frequency domains. Based on the projection lemma, a new partial multiplier expansion method is proposed to design state feedback controllers. The resulting sufficient conditions are given in terms of solutions to a set of linear matrix inequalities. Finally, the effectiveness of the proposed method is illustrated via a numerical design example.     

混合频小增益动态输出反馈控制综合

本文主要研究线性连续时间系统经动态输出反馈的混合频小增益控制综合问题. 提出了一种使相应闭环系统渐近稳定并满足有限频范围和全频范围小增益条件要求的动态输出反馈控制器的新设计方法. 设计条件以一系列线性矩阵不等式的解的形式给出. 最后, 给出一个数值例子来说明设计程序以及这种方法对比于现有方法的优势.     

Control synthesis via state feedback with finite frequency specifications for time-delay systems

This article considers the problem of control synthesis via state feedback for linear time-delay systems with design specifications in finite frequency ranges. First, a finite frequency performance analysis condition for time-delay systems is presented. Then, a resulting state feedback control synthesis condition is given in terms of solutions to a set of linear matrix inequalities (LMIs). Finally, the design procedure and the effectiveness of the proposed method are illustrated via a numerical design example.     

Output feedback control for MIMO non-linear systems with unknown sign of the high frequency gain matrix

The paper presents a new output feedback adaptive control scheme for multi-input and multi-output (MIMO) non-linear systems whose non-linear terms depend only on the output variable based on the backstepping approach with vector form. The assumption on the prior knowledge of the high frequency gain matrix in existing results is reduced and the new required condition for the high frequency gain matrix can be easily checked for certain plants so that the proposed method is widely applicable. This control scheme guarantees the global stability of the closed-loop systems and makes the tracking error be arbitrary small. A simulation example is included to demonstrate the proposed algorithm.     

Output feedback tracking control for lower‐triangular nonlinear time‐delay systems with asymmetric input saturation

In this paper, the problem of output feedback tracking control is investigated for lower‐triangular nonlinear time‐delay systems in the presence of asymmetric input saturation. A novel design program based on a dynamic high gain design approach is proposed to construct an output feedback tracking controller. The innovation here is that the problem of constructing tracking controller can be transformed into the problem of constructing two dynamic equations, with one being utilized to deal with the nonlinear terms and the other one being applied to analyze the influence of asymmetric input saturation. It is proved by an appropriate Lyapunov‐Krasovskii functional that the proposed tracking controller subject to saturation can ensure that all the signals of the closed‐loop system are globally bounded and the tracking error is prescribed sufficiently small when time is long enough. A practical example is given to illustrate the effectiveness of the proposed method.     

Global finite-time stabilization for a class of switched nonlinear systems via output feedback

This paper addresses the problem of global finite-time stabilization for a class of uncertain switched nonlinear systems via output feedback under arbitrary switchings. Based on the adding a power integrator approach, we design a homogeneous observer and controller for the nominal switched system without the perturbing nonlinearities. Then, a scaling gain is introduced into the proposed output feedback stabilizer to implement global finite-time stability of the closed-loop system. In addition, the proposed approach can be also extended to a class of switched nonlinear systems with upper-triangular growth condition. Two examples are given to illustrate the effectiveness of the proposed method.     

Adaptive neural output feedback tracking control for a class of nonlinear systems

In this paper, an adaptive neural output feedback control scheme based on backstepping technique and dynamic surface control (DSC) approach is developed to solve the tracking control problem for a class of nonlinear systems with unmeasurable states. Firstly, a nonlinear state observer is designed to estimate the unmeasurable states. Secondly, in the controller design process, radial basis function neural networks (RBFNNs) are utilised to approximate the unknown nonlinear functions, and then a novel adaptive neural output feedback tracking control scheme is developed via backstepping technique and DSC approach. It is shown that the proposed controller ensures that all signals of the closed-loop system remain bounded and the tracking error converges to a small neighbourhood around the origin. Finally, two numerical examples and one realistic example are given to illustrate the effectiveness of the proposed design approach.     

Robust near-optimal output feedback control of non-linear systems

This work proposes a robust near-optimal non-linear output feedback controller design for a broad class of non-linear systems with time-varying bounded uncertain variables. Both vanishing and non-vanishing uncertainties are considered. Under the assumptions of input-to-state stable (ISS) inverse dynamics and vanishing uncertainty, a robust dynamic output feedback controller is constructed through combination of a high-gain observer with a robust optimal state feedback controller synthesized via Lyapunov's direct method and the inverse optimal approach. The controller enforces exponential stability and robust asymptotic output tracking with arbitrary degree of attenuation of the effect of the uncertain variables on the output of the closed-loop system, for initial conditions and uncertainty in arbitrarily large compact sets, provided that the observer gain is sufficiently large. Utilizing the inverse optimal control approach and singular perturbation techniques, the controller is shown to be near-optimal in the sense that its performance can be made arbitrarily close to the optimal performance of the robust optimal state feedback controller on the infinite time-interval by selecting the observer gain to be sufficiently large. For systems with non-vanishing uncertainties, the same controller is shown to ensure boundedness of the states, uncertainty attenuation and near-optimality on a finite time-interval. The developed controller is successfully applied to a chemical reactor example.     

Distributed fuzzy adaptive event-triggered finite-time consensus tracking control for uncertain nonlinear multi-agent systems with asymmetric output constraint

This article investigates the consensus problem for uncertain nonlinear multi-agent systems (MASs) with asymmetric output constraint. Different from BLF-based constraint consensus tracking control, a novel approach based on nonlinear state-dependent function is proposed to solve the asymmetric output constraint, which need not convert output constraint into tracking error bound. First-order sliding mode differentiator is incorporated into each step of backstepping control design to reduce computation burden. Further, in combination of proposed event-triggered mechanism based on time-varying threshold, a distributed fuzzy adaptive event-triggered finite-time consensus method is developed. It can ensure that the consensus tracking error tends to a small neighbor in a finite time and the asymmetric output constraint of each subsystem is not violated. Two simulations are given to demonstrate the effectiveness of control method.     

Global control of nonlinear systems with uncertain output function using homogeneous domination approach

This paper addresses the problem of using output feedback to globally control a class of nonlinear systems whose output functions are not precisely known. First, for the nominal linear system, we design a homogeneous state compensator without requiring precise information of the output function, and construct a nonlinear stabilizer with adjustable coefficients by using the generalized adding a power integrator technique. Then based on the homogeneous domination approach, a scaling gain is introduced into the proposed output feedback controller, which can be used by tuning the scaling gain to solve: (i) the problem of global output feedback stabilization for a class of upper‐triangular systems; and (ii) the problem of global practical output tracking for a class of lower‐triangular systems. Copyright © 2011 John Wiley & Sons, Ltd.