Design of robust-optimal output feedback controllers for linear uncertain systems using LMI-based approach and genetic algorithm

This paper considers the robust-optimal design problems of output feedback controllers for linear systems with both time-varying elemental (structured) and norm-bounded (unstructured) parameter uncertainties. Two new sufficient conditions are proposed in terms of linear-matrix-inequalities (LMIs) for ensuring that the linear output feedback systems with both time-varying elemental and norm-bounded parameter uncertainties are asymptotically stable, where the mixed quadratically-coupled parameter uncertainties are directly considered in the problem formulation. A numerical example is given to show that the presented sufficient conditions are less conservative than existing ones reported recently. Then, by integrating the hybrid Taguchi-genetic algorithm (HTGA) and the proposed LMI-based sufficient conditions, a new integrative approach is presented to find the output feedback controllers of the linear systems with both time-varying elemental and norm-bounded parameter uncertainties such that the control objective of minimizing a quadratic integral performance criterion subject to the stability robustness constraint is achieved. A design example of the robust-optimal output feedback controller for the AFTI/F-16 aircraft control system with the time-varying elemental parameter uncertainties is given to demonstrate the applicability of the proposed new integrative approach.     

具有快变时延和丢包的网络控制系统镇定

对一类网络控制系统,研究了变时延和数据丢包对闭环系统稳定性的影响.基于Lyapunov-Krasovskii方法,给出了闭环系统的稳定条件,该条件不依赖于时延变化率的上界.通过求解一个适当的线性矩阵不等式(LMI)得到控制增益矩阵,求解时不需要对矩阵的结构进行限制,也不必使用重复迭代.最后,给出了一个数值例子以说明方法的有效性.     

Estimation of stability of oscillations of linear time-varying systems with one time-varying parameter with calculation of influence of higher frequency motions

The paper reveals a new method for estimation of stability of oscillations of linear time invariant systems with one time-varying parameter given by a harmonic function. The suggested approach includes building a matrix of transfer functions, which calculates interference of the highfrequency oscillations of the output of the linear time-invariant part of the system. Suggested approach makes possible to build equivalent of the Nyquist criterion for linear systems with a single time-varying parameter. The application of the suggested approach is shown by numerical examples. Results of the present article may be used for control systems of cranes and other lifting mechanisms.     

Input-to-state stability for networked control systems via an improved impulsive system approach

This paper presents a novel impulsive system approach to input-to-state stability (ISS) analysis of networked control systems (NCSs) with time-varying sampling intervals and delays. This approach is based upon the new idea that an NCS can be viewed as an interconnected hybrid system composed of an impulsive subsystem and an input delay subsystem. A new type of time-varying discontinuous Lyapunov-Krasovskii functional, which makes full use of the information on the piecewise-constant input and the bounds of the network delays, is introduced to analyze the ISS property of NCSs. Linear matrix inequality based sufficient conditions are derived for ISS of NCSs with respect to external disturbances. When applied to the approximate tracking problem for NCSs, the derived ISS result provides bounds on the steady-state tracking error. Numerical examples are provided to show the efficiency of the proposed approach.     

Stability analysis of networked control systems with time-varying sampling periods

In this paper, we present an interval model of networked control systems with time-varying sampling periods and time-varying network-induced delays and discuss the problem of stability of networked control systems using Lyapunov stability theory. A sufficient stability condition is obtained by solving a set of linear matrix inequalities. In the end, the illustrative example demonstrates the correctness and effectiveness of the proposed approach.     

Stability analysis for continuous systems with two additive time-varying delay components

This paper presents a new result of stability analysis for continuous systems with two additive time-varying delay components, which represent a general class of delay systems with strong application background in network based control systems. This criterion is expressed as a set of linear matrix inequalities, which can be readily tested by using standard numerical software. A numerical example is provided to show the effectiveness and advantage of the proposed stability condition.     

改进的时延丢包网络控制系统的分析和控制

将网络控制系统建模为时变时滞系统模型,考虑有界、时变时延和丢包的网络控制系统的稳定性分析和控制器设计问题。首先构造一个新的分段Lyapunov-Krasovskii泛函,充分利用时延上下界信息,然后结合更紧的有限和不等式处理时滞区间,得到具有较小保守性的稳定性准则,基于一种改进的锥补线性化迭代算法给出状态反馈器设计方法,证明中没有引进模型变换和自由矩阵,减少了计算上的复杂性。通过实例表明上述方法的有效性。     

Stability problem of a periodically varying system

In this paper we investigate the problem of stability for periodically time-varying systems. This study is needed, for instance, to determine robustness and stability of repetitive learning systems used in the control of complex systems such as robotic manipulators. We use classical and new results for the stability of linear time-varying systems to re-establish an upper bound on the rate of parameter variations of the periodically time-varying systems, We then examine in detail the effects of these variations on the asymptotic and exponential stability of a special class of systems.     

线性多时变时滞系统的指数稳定性

本文基于一个新型滞后动态系统指数稳定性定理和两个准备引理, 采用 Lyapunov 函数稳定性分析新方法, 建立了线性多时变时滞系统保守性少的稳定性条件. 与文献中已有的一些结果不同, 所建立的稳定性条件不依赖于时变时滞的变化率. 因此, 所建立的结果适用于具有非常快变时滞的系统. 文中给出了一个例子展示所得结果好于直接采用标准的 Razumikhin 型条件所得的结果.     

Further results on strict Lyapunov functions for rapidly time-varying nonlinear systems

We explicitly construct global strict Lyapunov functions for rapidly time-varying nonlinear control systems. The Lyapunov functions we construct are expressed in terms of oftentimes more readily available Lyapunov functions for the limiting dynamics which we assume are uniformly globally asymptotically stable. This leads to new sufficient conditions for uniform global exponential, uniform global asymptotic, and input-to-state stability of fast time-varying dynamics. We also construct strict Lyapunov functions for our systems using a strictification approach. We illustrate our results using several examples.     

Stability analysis of systems via a new double free-matrix-based integral inequality with interval time-varying delay

ABSTRACT

This paper investigates the problem of delay-dependent stability analysis for systems with interval time-varying delay. By means of a new double free-matrix-based integral inequality and augmented Lyapunov–Krasovskii functionals containing as much information of time-varying delay as possible, a new stability criterion for systems is established. Firstly, by a double integral term two-step estimation approach and combined with single free-matrix-based integral inequalities, a stability criteria is presented. Then, compared with the double integral term two-step estimation approach, the proposed new double free-matrix-based integral inequality with more related time delays has potential to lead to a criterion with less conservatism. Finally, the validity of the presented method is demonstrated by two numerical examples.     

Decoupling and tracking control using eigenstructure assignment for linear time-varying systems

This work is concerned with the assignment of a desired PD-eigenstructure for linear time-varying systems. Despite its well-known limitations, gain scheduling control appeared to be a focus of the research efforts. Scheduling of frozen-time, frozen-state controllers for fast time-varying dynamics is known to be mathematically fallacious, and practically hazardous. Therefore, recent research efforts are being directed towards applying time-varying controllers. In this paper, (a) we introduce a differential algebraic eigenvalue theory for linear time-varying systems, and then (b) a novel decoupling and tracking control scheme is proposed by using the PD-eigenstructure assignment scheme via a differential Sylvester equation and a Command Generator Tracker for linear time-varying systems. The PD-eigenstructure assignment is utilized as a regulator. A feedforward gain for tracking control is computed by using the command generator tracker. The whole design procedure of the proposed PD-eigenstructure assignment scheme is systematic in nature. The scheme could be used to determine stability of linear time-varying systems easily as well as to provide a new horizon of designing controllers for the linear time-varying systems. The presented method is illustrated by numerical examples.     

带有干扰的线性时变系统的非线性鲁棒控制

研究了含有未知时变参数和有界干扰的单输入单输出线性时变系统的鲁棒控制问题.系统时变参数只要求光滑有界而不限制为慢时变或参数上界已知.利用时变的状态变换得到新的动态系统,基于Backstepping方法,设计出一种非线性鲁棒控制器.通过适当选择控制器参数,可以保证闭环系统是全局渐近稳定的.仿真例子表明了算法的有效性.     

一类区间时变时滞系统的稳定性分析

针对一类区间时变时滞系统的稳定性问题,进行了全局渐近稳定性分析.通过引入时滞分段方法和构建恰当的Lyapunov-Krasovskii泛函,得到了新的区间时滞相关稳定性判定准则.该准则以线性矩阵不等式形式给出,便于利用LMI工具箱对系统的稳定性进行判定.新准则具有较少的保守性,并且在一定范围内保守性随着时滞分段增多而减少,即时滞分段越多,保守性越少.数值仿真算结果例表明了新准则所具有的有效性和较少的保守性.     

A new periodic adaptive control approach for time-varying parameters with known periodicity

A new adaptive control approach is proposed to deal with nonlinear systems with a class of time-varying parametric uncertainties, which are in an unknown compact set, periodic, nonvanishing, rapid time-varying, and the only prior knowledge is the periodicity. Unlike most continuous time adaptation laws which are of differential types, in this work a periodic type adaptation law is introduced for continuous time systems. The new adaptive controller updates the parameters and the control signal periodically in a pointwise manner over one entire period, in the sequel achieves the asymptotic tracking convergence.     

关于自适应控制系统的鲁棒稳定性条件

本文用统一的方法对于由自适应控制系统的鲁棒稳定性分析提出的一类时变动态系统的有界解问题给出了一个充分条件。它为鲁棒自适应控制器的设计以及进行相应的理论分析带来了方便。     

Lotka-Volterra-like approach to large-scale systems stability

A new aggregation form of large-scale systems is proposed in this paper. It is of the ‘Lotka-Volterra’ type and appears natural for the generalized Lotka-Volterra large-scale (possibly time-varying) systems, which is shown in the paper. The Lotka-Volterra aggregation form yields a comparison system of the generalized Lotka-Volterra type, which is composed of a linear and a non-linear part. In addition this aggregation form leads to new stability conditions for time-varying large-scale systems, and enables an extension of Weissenberger's results on exponential stability domain estimates to the asymptotic stability domain estimate of time-varying systems. An advantageous feature of the system aggregation and stability analysis developed in the paper is the omission of requirements for (any particular, e.g. exponential) stability of disconnected subsystems.     

Stability of non-linear feedback systems with time-varying linear sub-system (plant) †

A new approach is used to examine the stability of feedback systems comprising a time-varying linear subsystem and a time-varying non-linearity. The paper examines three stability aspects of the systems dynamic response: boundedness, unboundedness, and asymptotic decay. In addition to qualitative criteria, the results provide explicit quantitative bounds on the system response. The distinct time-domain method of analysis presented stipulates rather weak a priori restrictions on the nature of the linear and non-linear parts of the system, thus admitting a relatively broad class of systems. In the general time-varying non-linear feedback system considered, the non-linearity may exhibit hysteresis, and the linear subsystem may be non-causal, and may comprise any number of feed-forward differentiators of any order. The criteria obtained are given a simple graphical interpretation. A transformation which trades time-varying gains between plant and non-linearity is introduced. A number of examples demonstrate that the present results can predict stability information not obtainable from other existing criteria. In one example of a system with stationary plant, the present criteria prove superior to the Circle Theorem.     

Observer-based state tracking control of uncertain stochastic systems via repetitive controller

This paper develops the repetitive control scheme for state tracking control of uncertain stochastic time-varying delay systems via equivalent-input-disturbance approach. The main purpose of this work is to design a repetitive controller to guarantee the tracking performance under the effects of unknown disturbances with bounded frequency and parameter variations. Specifically, a new set of linear matrix inequality (LMI)-based conditions is derived based on the suitable Lyapunov–Krasovskii functional theory for designing a repetitive controller which guarantees stability and desired tracking performance. More precisely, an equivalent-input-disturbance estimator is incorporated into the control design to reduce the effect of the external disturbances. Simulation results are provided to demonstrate the desired control system stability and their tracking performance. A practical stream water quality preserving system is also provided to show the effectiveness and advantage of the proposed approach.     

New stability criteria for singular systems with time-varying delay and nonlinear perturbations

This paper concerns the stability analysis for singular systems with time-varying delay and nonlinear perturbations. Two cases of time-varying delay, which is differentiable (Case 1) or not differentiable (Case 2), are considered. The considered nonlinear perturbations includes the norm-bounded uncertainties as a special case. Some delay-dependent stability criteria are derived by using a delay decomposition approach. In the delay decomposition approach, the entire delay interval is divided into multiple sub-intervals for which different energy functions are defined for building new Lyapunov–Krasovskii functional. Some numerical and practical examples are given to show the effectiveness and significant improvement of the proposed method.