Frequency-domain $L_2$-stability conditions for time-varying linear and nonlinear MIMO systems

The paper deals with the g2-stability analysis of multi-input-multi-output （MIMO） systems, governed by integral equations, with a matrix of periodic/aperiodic time-varying gains and a vector of monotone, non-monotone and quasi-monotone nonlin- earities. For nonlinear MIMO systems that are described by differential equations, most of the literature on stability is based on an application of quadratic forms as Lyapunov-function candidates. In contrast, a non-Lyapunov framework is employed here to derive new and more general g2-stability conditions in the frequency domain. These conditions have the following features： i） They are expressed in terms of the positive definiteness of the real part of matrices involving the transfer function of the linear time-invariant block and a matrix multiplier function that incorporates the minimax properties of the time-varying linear/nonlinear block, ii） For certain cases of the periodic time-varying gain, they contain, depending on the multiplier function chosen, no restrictions on the normalized rate of variation of the time-varying gain, but, for other periodic/aperiodic time-varying gains, they do. Overall, even when specialized to periodic-coefficient linear and nonlinear MIMO systems, the stability conditions are distinct from and less restrictive than recent results in the literature. No comparable results exist in the literature for aperiodic time-varying gains. Furthermore, some new stability results concerning the dwell-time problem and time-varying gain switching in linear and nonlinear MIMO systems with periodic/aperiodic matrix gains are also presented. Examples are given to illustrate a few of the stability theorems.     

Vague关系的α-分解

提出了Vague关系R是可α-分解的概念。得到Vague关系R是可α-分解的两个等价刻画。在Vague关系R是可α-分解时,分别给出了使R=AαB成立的A与B的解集。     

GPG-stability of Runge-Kutta methods for generalized delay differential systems

The GP_G-stability of Runge-Kutta methods for the numerical solutions of the systems of delay differential equations is considered. The stability behaviour of implicit Runge-Kutta methods (IRK) is analyzed for the solution of the system of linear test equations with multiple delay terms. After an establishment of a sufficient condition for asymptotic stability of the solutions of the system, a criterion of numerical stability of IRK with the Lagrange interpolation process is given for any stepsize of the method.     

Oscillation,stability, and boundedness of second-order differential systems with random impulses

The model of second-order linear differential systems with random impulses is brought forward in this paper. Then, necessary and sufficient conditions for oscillation in mean, p-moment stability and p-moment boundedness are obtained by several theorems that compare solutions of this system with the corresponding nonimpulsive differential system. At last, an example is presented to show the application of obtained results.     

Impulsive control of unstable neural networks with unbounded time-varying delays

This paper considers the impulsive control of unstable neural networks with unbounded time-varying delays, where the time delays to be addressed include the unbounded discrete time-varying delay and unbounded distributed time-varying delay. By employing impulsive control theory and some analysis techniques, several sufficient conditions ensuring μ-stability, including uniform stability, (global) asymptotical stability, and (global) exponential stability, are derived. It is shown that an unstable delay neural network, especially for the case of unbounded time-varying delays, can be stabilized and has μ-stability via proper impulsive control strategies. Three numerical examples and their simulations are presented to demonstrate the effectiveness of the control strategy.     

Characterizations of regular ordered semigroups in terms of (α, β)-fuzzy generalized bi-ideals

In this paper, the concept of an (α, β)-fuzzy generalized bi-ideal in an ordered semigroup is introduced, which is a generalization of the concept of a fuzzy generalized bi-ideal in an ordered semigroup. Using this concept, some characterization theorems are provided. The upper/lower parts of an (∈, ∈ ∨ q)-fuzzy generalized bi-ideal are introduced and some characterizations of regular ordered semigroups are given. Also, we consider the concept of implication-based fuzzy generalized bi-ideals in an ordered semigroup. In particular, the implication operators in Lukasiewicz system of continuous-valued logic are discussed.     

Absolute stability criteria with prescribed decay rate for finite-dimensional and delay systems

We provide here an extension of Popov criterion, permitting to check exponential stability with prescribed decay rate (otherwise called α-stability) of nonlinear delay systems with sector-bounded nonlinearities. As for the celebrated result, the main hypothesis is expressed under a frequency form. For the delay-free case, the latter is equivalent to a linear matrix inequality, whose solution may be found by widespread algorithms.     

Exponential p-stability of second order Cohen–Grossberg neural networks with transmission delays and learning behavior

In this paper, we investigate second order Cohen–Grossberg neural networks with transmission delays and an unsupervised Hebbian-type learning behavior. By using Laypunov–Krasovskii functional, some new sufficient conditions are established for the existence and global exponential p-stability of a unique equilibrium without strict conditions imposed on self regulation functions. The obtained sufficient conditions are easy to verify and our results improve the previously known results. Finally, computer simulations are performed to illustrate exponential p-stability of equilibrium and learning dynamic behavior of neurons.     

Dissipative stability analysis and control of two-dimensional Fornasini–Marchesini local state-space model

This paper is concerned with the problems of dissipative stability analysis and control of the two-dimensional (2-D) Fornasini–Marchesini local state-space (FM LSS) model. Based on the characteristics of the system model, a novel definition of 2-D FM LSS (Q, S, R)-α-dissipativity is given first, and then a sufficient condition in terms of linear matrix inequality (LMI) is proposed to guarantee the asymptotical stability and 2-D (Q, S, R)-α-dissipativity of the systems. As its special cases, 2-D passivity performance and 2-D H_∞ performance are also discussed. Furthermore, by use of this dissipative stability condition and projection lemma technique, 2-D (Q, S, R)-α-dissipative state-feedback control problem is solved as well. Finally, a numerical example is given to illustrate the effectiveness of the proposed method.     

Guardian map approach to robust stability of interval systems

A systematic approach for the robust Hurwitz and Schur stability of the dynamic interval systems is proposed. An interval matrix is expressed as a linear fractional transformation (LFT) of an interconnection matrix with structured real parametric uncertainties. Based on guardian map theory and µ-analysis, a new approach is provided to derive the necessary and sufficient conditions in terms of the structured singular value (μ) ensuring the stability robustness of interval systems. This approach is feasible for both continuous- and discrete-time interval systems by a unified LFT framework, and it is applicable directly to D-stability for performance requirements.     

Stability,transient behaviour and trajectory bounds of interconnected systems†

In practice, many systems are complex and of high dimension. Many such systems may be viewed as being composed of several simpler sub-systems which when connected in an appropriate fashion yield the original composite system. The stability, the transient behaviour and estimates for the trajectory bounds of certain composite systems are analysed in terms of their sub-systems. This is accomplished by defining the stability of sub-systems and of composite systems in terms of certain time-varying sub-sets of the state space which are pre-specified in a given problem.

After stating definitions of stability for sub-systems which are under the influence of perturbing forces and for composite systems, theorems are stated and proved which yield sufficient conditions for stability. These theorems involve the existence of Lyapunov-like functions which do not possess any particular definiteness requirements on V and [Vdot].

The time-varying sub-sets of the state space which are utilized in the stability definitions and which arise in conjunction with the stability theorems yield estimates of the transient behaviour and of the trajectory bounds of both sub-systems and composite systems.

To demonstrate the generality of the developed theory, several special cases are considered. Also, some specific examples are worked out to demonstrate the methods involved.     

Stability and robustness for nonlinear systems decoupled and linearized by feedback

We give some stability and robustness results for nonlinear systems which are transformed by feedback and immersion into decoupled linear systems. In particular we give a necessary condition involving the Euler-Poincaré characteristic of asymptotic unobservable submanifolds. This condition is successfully applied to a non-minimum-phase example (see Byrnes and Isidori [2]) borrowed from robotics which displays K-stability.     

Stability analysis of sampled-data systems via open-/closed-loop characteristic polynomials contraposition

In this paper, a class of sampled-data systems with double feedbacks are scrutinized for internal/external stability through the open-/closed-loop characteristic polynomials contraposition. A sampled-data system with double feedbacks consists of a continuous-time plant and two feedback control loops: a discrete-time one for digital control objectives with sampler and zero-order hold synchronized, and a continuous-time one for analog control performances. Contraposition stability criteria are worked out by exploiting what we call the contraposition return difference relationship in between the open- and closed-loop characteristic polynomials defined via the lifted model. The criteria for asymptotical stability are necessary and sufficient, independent of open-loop poles distribution of the lifted model and locus orientation specification. Moreover, the criteria for L_p-stability are sufficient, while retaining the technical merits of the criteria for asymptotical stability. All criteria present stability conditions in the standard discrete-time sense that are implementable either graphically with loci plotting, or numerically without loci plotting. Examples are included to illustrate the results.     

High-order stiffly stable methods for analysis of non-linear circuits and systems

Two easy-to-check conditions are given which, together, are sufficient conditions for A₀ stability, A(0)-stability and stiff stability of linear multistep integration formulae. As an example, these conditions are applied to high-order stiffly stable operators developed by Dill and Gear, and by Jain and Srivastava.     

参数LP系统的三I算法与α-三I算法

给出了连续三角模族T_(p-L)及其伴随蕴涵算子族R_(p-L)的定义,并且给出了逻辑系统LP的定义;证明了逻辑系统LP与逻辑系统L的等价性,在此基础上给出了基于蕴涵算子族R_(p-L)的三I算法与α-三I算法。     

基于蕴涵算子族L-λ-R_0的模糊推理FMT三Ⅰ算法

提出了基于蕴涵算子族L-λ-R0的模糊推理的思想,这将有助于提高推理结果的可靠性。针对蕴涵算子族L-λ-R0已给出的FMP模型[1]的三Ⅰ支持算法、α-三Ⅰ支持算法进一步给出了模糊推理的FMT模型的三Ⅰ支持算法、α-三Ⅰ支持算法。     

Robust finite time stability of fractional-order linear delayed systems with nonlinear perturbations

This letter is concerned with robust stability of fractional-order linear delayed system with nonlinear perturbations over finite time interval. By using inequality technique, two new sufficient conditions for the finite time stability for such systems with order α: 0 α ≤ 0.5 and 0.5 < α < 1 are presented, respectively. A numerical example is presented to demonstrate the validity and feasibility of the obtained results.     

ρ-Stability and robustness: discrete-time case

We say that a discrete-time system is ρ-stable if, roughly speaking, ρ^k >X _k→0, where >X _k is the system state. General ρ-stability theorems are established in this paper. They concern systems governed by functional difference equations. Systems of this type are encountered in the robustness studies. These ρ-stability theorems are a generalization of the well-known Lyapunov criterion. These results are applied to the robustness quantification problem in the second part of the paper. The case of discrete-time LQ regulators is deeply investigated. Robustness properties of continuous-time LQ regulators are found as the limit when the sampling period >T tends to zero; robustness deteriorates as T increases. An upper bound is given for >T, under which the robustness remains satisfactory. The practical interest of these theoretical results is illustrated on the basis of an industrial example.     

Necessary and sufficient stability condition of fractional-order interval linear systems

This paper establishes a necessary and sufficient stability condition of fractional-order interval linear systems. It is supposed that the system matrix A is an interval uncertain matrix and fractional commensurate order belongs to 1≤α<2. Using the existence condition of Hermitian P=P^∗ for a complex Lyapunov inequality, we prove that the fractional-order interval linear system is robust stable if and only if there exists Hermitian matrix P=P^∗ such that a certain type of complex Lyapunov inequality is satisfied for all vertex matrices. The results are directly extended to the robust stability condition of fractional-order interval polynomial systems.     

Practical ϕ 0-stability of switched stochastic nonlinear systems and corresponding stochastic perturbation theory

The aim of this paper is to study the practical ф0 -stability in probability (Pф0 SiP) and practical ф0 -stability in pth mean (Pф0 SpM) of switched stochastic nonlinear systems. Sufficient conditions on such practical properties are obtained by using the comparison principle and the cone-valued Lyapunov function methods. Also, based on an extended comparison principle, a perturbation theory of switched stochastic systems is given.