Stability analysis and design of Takagi-Sugeno fuzzy systems

This work presents stable composite control criteria for multivariable Takagi-Sugeno (T-S) fuzzy systems. On the basis of the linear matrix inequality (LMI) control strategy and parametric optimization, the composite fuzzy control algorithms are derived. Unlike earlier studies of fuzzy control systems on an LMI framework, this investigation develops a supervisory control approach, such that a fuzzy controller can be synthesized more efficiently. Moreover, a robust control scheme is applied to the T-S fuzzy model with parametric uncertainties. The sufficient conditions are deduced in the form of reduced LMIs and adaptive tuning rules. Finally, numeric simulations are given to validate the proposed approach.     

Analysis and synthesis of nonlinear time-delay systems via fuzzycontrol approach

Takagi-Sugeno (TS) fuzzy models (1985, 1992) can provide an effective representation of complex nonlinear systems in terms of fuzzy sets and fuzzy reasoning applied to a set of linear input/output (I/O) submodels. In this paper, the TS fuzzy model approach is extended to the stability analysis and control design for both continuous and discrete-time nonlinear systems with time delay. The TS fuzzy models with time delay are presented and the stability conditions are derived using Lyapunov-Krasovskii approach. We also present a stabilization approach for nonlinear time-delay systems through fuzzy state feedback and fuzzy observer-based controller. Sufficient conditions for the existence of fuzzy state feedback gain and fuzzy observer gain are derived through the numerical solution of a set of coupled linear matrix inequalities. An illustrative example based on the CSTR model is given to design a fuzzy controller     

Invertibility of observable multivariable nonlinear systems

Based on the algorithm of Hirschorn [1] for obtaining inverses, sufficient conditions for invertibility of observable multivariable nonlinear systems are derived. For observable and invertible systems, a static left-inverse system is constructed. For certain noninvertible systems, the sufficient condition yields a characterization of input space on which the input-output map is injective.     

Invertibility of multivariable nonlinear control systems

This paper gives sufficient conditions for the invertibility of nonlinear control systems of the formdot{x}= A(x)+ u_{1}B_{1}(x) +... + u_{m} B_{m}(x);y=c(x), where the state space is a real analytic manifold. These conditions are also necessary in the case of single-input nonlinear systems and multivariable time-invariant linear systems. For invertible systems we construct nonlinear inverse systems.     

T-S模糊系统输出反馈控制器的稳定性分析与设计

输出反馈控制是T-S模糊控制系统设计的一种重要方法．本文提出了一类由模糊状态观测器和模糊调节器构成的输出反馈控制器稳定性分析和解析设计的新方法．为了减小稳定性分析的保守性和难度,本文充分利用了模糊规则前件变量模糊隶属度函数的结构信息,对前件变量采用标准模糊分划的T-S模糊系统输出反馈控制器进行了研究,获得了一些新的稳定性条件．然后采用平行分布补偿法(PDC)和线性矩阵不等式方法(LMI),研究了该类输出反馈控制器的解析设计方法．通过一个非线性质量块-弹簧-阻尼器系统输出反馈控制器的设计和计算机仿真,验证了本文方法的有效性．     

一类T-S模糊控制系统的稳定性分析及设计

研究了一类输入采用双交叠模糊分划的T-S模糊控制系统稳定性分析及控制器设计问题.基于分段模糊Lyapunov函数,提出了一个新的判定开环T-S模糊系统稳定性的充分条件,该方法只需在各个模糊区间里满足模糊Lyapunov方法中的条件,其保守性比公共Lyapunov函数法和分段Lyapunov函数法的保守性更低.运用并行分布补偿法(PDC)进一步探讨了闭环T-S模糊控制系统的稳定性分析问题并设计了模糊控制器.最后,一个仿真示例说明了本文方法的有效性.     

Adaptive control of a class of multivariable nonlinear systems andconvergence analysis

Adaptive control is discussed of a class of multivariable nonlinear systems which can be characterized by a stochastic multivariable Hammerstein model whose linear part possesses an arbitrary interactor matrix. A simple suboptimal control law is derived which provides an efficient way to control a multivariable Hammerstein model whose linear part is not necessarily minimum phase. A direct adaption scheme is presented to implement the control law, and the global convergence of the algorithm is established     

Stability analysis of distributed-order nonlinear dynamic systems

The problem of asymptotic stability analysis of equilibrium points in nonlinear distributed-order dynamic systems with non-negative weight functions is considered in this paper. The Lyapunov direct method is extended to be used for this stability analysis. To this end, at first, a discretisation scheme with convergence property is introduced for distributed-order dynamic systems. Then, on the basis of this tool, Lyapunov theorems are proved for asymptotic stability analysis of equilibrium points in distributed-order systems. As the order weight function assumed for the distributed-order systems is general enough, the results are applicable to a wide range of nonlinear distributed-order systems such as fractional-order systems with multiple fractional derivatives. To verify the applicability of the obtained results, these results are applied for the stability analysis of a distributed-order diffusion system and control of a fractional-order Lorenz system with multiple fractional derivatives.     

An anti-windup scheme for multivariable nonlinear systems

In this paper, an approach to control synthesis for constrained multivariable nonlinear systems using feedback linearization is described. The synthesis of a multivariable saturation element which preserves the directionality of the input vector and produces control action which upholds constraints within the original coordinate system is discussed. Nominal stability analysis is performed using nonlinear μ-analysis for a restricted region of the state-space. A set of conditions is obtained which defines the region of the state space over which the stability analysis is applicable. The results are applied to both a numerical example and to a multivariable polymerization reactor model.     

Stability analysis of nonlinear multiparameter singularly perturbed systems

Asymptotic stability of nonlinear multiparameter singularly perturbed systems is analyzed. Sufficient conditions for existence of a Lyapunov function and uniform asymptotic stability are derived. The new feature of these conditions over earlier results is that there is no restriction on the relative magnitudes of the small singular perturbation parameters. Moreover, the class of systems under consideration can be nonlinear in both the slow and fast variables, while earlier results were limited to systems linear in the fast variables.     

Stability analysis of complex-valued nonlinear delay differential systems

Since a quantum system, which is one of the foci of ongoing research, is a classical example of a complex-valued system, in this paper, the issue of asymptotic stability of solutions to complex-valued nonlinear delay differential systems is addressed. By taking advantage of the theory of matrix measure, the exponential stability criteria of a complex-valued nonlinear delay system are established, which not only improve some known results in literature, but also greatly reduce the complexity of analysis and computation. As an application, the exponential stability conditions of 2-dimensional real-valued time-varying delay systems are derived, the conditions are easier to verify in comparison with known results. The effectiveness of the main results are illustrated by some numerical examples.     

Stability analysis for 2-D switched Takagi-Sugeno fuzzy systems with stable and unstable subsystems

This paper is concerned with the problem of stability of two-dimensional (2-D) switched Takagi-Sugeno (T-S) fuzzy systems with stable and unstable subsystems described by the Roesser model with constant delays. The T-S fuzzy model is applied to close the discrete-time nonlinear subsystems. By utilizing the definitions of mode-dependent average dwell time (MDADT) method and a quasi-alternative switching signal, the stability condition for 2-D discrete-time switched systems composed of stable and unstable subsystems is derived, and a study on one-dimentional (1-D) system can be seen as a special case. Finally, the effectiveness and advantage of the obtained results are illustrated through practical example by LMI toolbox.     

Time domain stability concepts for multivariable nonlinear systems

This work presents bounded-input bounded-output and asymptotic stability criteria for multivariable systems with feedback nonlinearity. The approach is in the time domain and relates the nonlinear system's stability properties to certain important linearized system parameters. The stability criteria are particularly applicable to the analysis and design of nonlinear systems via linearization.     

基于T- S模型的非线性系统多模型直接自适应控制

针对典型的高阶非线性系统，建立被控对象的多个论域不同的基于T—S模型的模糊控制器(TSFC)，用其加权组合控制系统的行为，并报据Lyapunov的综合方法设计一种自适应算法来调整每个TSFC的权值，形成被控对象的直接自适应模糊控制器。与采用单一TSFC的自适应模糊控制算法相比，该算法计算量小，响应速度快，能在局部上更有效地控制系统的非线性，使被控系统具有Lyapunov意义上的稳定性。仿真实验证实了算法的有效性。     

Input/output characterization of highly nonlinear multivariable systems

This paper presents a software in the MATLAB environment for input/output characterization of highly nonlinear multivariable systems. The software is based on obtaining the sinusoidal-input describing function (SIDF) models of the nonlinear multivariable plant. The mathematical development of the input/output characterization approach is outlined, and the printout of the nucleus of the characterization software is given. The method and the associated software have no restriction on nonlinearity type, configuration, and arrangement, system order as well as the number of inputs and outputs; the only requirement is that system output(s) for sinusoidal input(s) must be obtainable or available by either simulation or experiments. The software has a variety of applications in such industries as robotics, aerospace, automotive, and chemical processes. The method and the associated software are demonstrated by solving a problem of the sort encountered in aerospace.     

Input-output linearization of nonlinear systems using multivariable Legendre polynomials

This contribution presents a new approach for the numeric computation of the input-output linearizing feedback law, which is obtained exactly in an analytical form. By using a state space embedding technique the nonlinear system to be controlled is described by a higher order system with solely polynomial nonlinearities. Consequently, the nonlinearities of this system can be represented by multivariable Legendre polynomials, so that the derivation of the input-output linearizing feedback controller can be accomplished using the operational matrices of multiplication and of differentiation for Legendre polynomials.     

On the stability of symmetric nonlinear output-coupled multivariable systems

A Lyapunov function together with a modified Meyer-Kalman-Yakubovitch lemma are used to develop absolute stability conditions for autonomous symmetric nonlinear output-coupled multivariable systems. The nonlinear characteristics are restricted in both sector and slope. As an example, a coupled-core nuclear reactor with typical parameters is considered to illustrate the concepts developed in this correspondence.     

Stability analysis for a class of switched nonlinear systems

This paper addresses the stability analysis of a class of switched nonlinear systems. The switched systems have uncertain nonlinear functions constrained in a sector set, which are called admissible sector nonlinearities. A sufficient condition in terms of linear inequalities is presented to guarantee the existence of a common Lyapunov function, and thereby to ensure that the switched system is stable for an arbitrary switching signal and any admissible sector nonlinearities. A constructive algorithm based on the modified Gaussian elimination procedure is given to find the solutions of the linear inequalities. The obtained results are applied to a population model with switchings of parameter values and the conditions of ultimate boundedness of its solutions are investigated. Another example of an automatic control system is considered to demonstrate the effectiveness of the proposed approaches.