Allowable delay sets for the stability analysis of linear time-varying delay systems using a delay-dependent reciprocally convex lemma

This paper develops a quadratic function convex approximation approach to deal with the negative definite problem of the quadratic function induced by stability analysis of linear systems with time-varying delays. By introducing two adjustable parameters and two free variables, a novel convex function greater than or equal to the quadratic function is constructed, regardless of the sign of the coefficient in the quadratic term. The developed lemma can also be degenerated into the existing quadratic function negative-determination (QFND) lemma and relaxed QFND lemma respectively, by setting two adjustable parameters and two free variables as some particular values. Moreover, for a linear system with time-varying delays, a relaxed stability criterion is established via our developed lemma, together with the quivalent reciprocal combination technique and the Bessel-Legendre inequality. As a result, the conservatism can be reduced via the proposed approach in the context of constructing Lyapunov-Krasovskii functionals for the stability analysis of linear time-varying delay systems. Finally, the superiority of our results is illustrated through three numerical examples.

Stability analysis of linear systems subject to regenerative switchings

This paper is concerned with the delay-dependent stability analysis of linear systems with a time-varying delay. Two types of improved Lyapunov-Krasovskii functionals (LKFs) are developed to derive less conservative stability criteria. First, a new delay-product-type LKF, including single integral terms with time-varying delays as coefficients is developed, and two stability criteria with less conservatism due to more delay information included are established for different allowable delay sets. Second, the delay-product-type LKF is further improved by introducing several negative definite quadratic terms based on the idea of matrix-refined-function-based LKF, and two stability criteria with more cross-term information and less conservatism for different allowable delay sets are also obtained. Finally, a numerical example is utilized to verify the effectiveness of the proposed methods.

Stability analysis of linear systems with two additive time-varying delays via delay-product-type Lyapunov functional

The main objective of this paper is to present the time domain, frequency domain and stability analysis of linear systems represented by differential equations with complex-order derivatives. The impulse and step response of three different complex-order systems have been presented numerically with the help of MATLAB. For frequency domain analysis, Bode-plots of the same three complex-order systems have been sketched. Complex-order systems have infinite numbers of complex-conjugate poles. The stability analysis of the complex-order systems has been done in two ways. Firstly, for systems to be stable, the complex-conjugate poles in the principle Riemann sheet must be in the left half plane. Secondly, the complex-order q = u + iv of the complex-order systems must be interior to an open disk in the u-v plane, for systems to be stable.

Multiple-integral inequalities to stability analysis of linear time-delay systems

This paper addresses the stability analysis of linear continuous systems under interval uncertainties. An interval generalization of the known Raus criterion is suggested to estimate the stability of the system considered. It is based on obtaining the interval extensions of the elements of the Raus matrix which are nonlinear functions of independent system parameters. The case when these elements are independent intervals is considered. The interval extensions are also determined by using modified affine arithmetic. Two sufficient conditions on stability and instability of the linear system considered are obtained. A numerical example illustrating the applicability of the method suggested is solved at the end of the paper.

This paper proposes novel single and double integral inequalities with arbitrary approximation order by employing shifted Legendre polynomials and Cholesky decomposition, and these inequalities could significantly reduce the conservativeness in stability analysis of linear systems with interval time-varying delays. The coefficients of the proposed single and double integral inequalities are determined by using the weighted least-squares method. Also former well-known integral inequities, such as Jensen inequality, Wirtinger-based inequality, auxiliary function-based integral inequalities, are all included in the proposed integral inequalities as special cases with lower-order approximation. Stability criterions with less conservatism are then developed for both constant and time-varying delay systems. Several numerical examples are given to demonstrate the effectiveness and benefit of the proposed method.

Improved results on stability of linear systems with time-varying delays via Wirtinger-based integral inequality

This work introduces novel results on the stability of linear time-varying discrete-time delay systems, addressing both internal stability and input-to-state stability. We start from the special case of positive delay systems and provide conditions of global exponential stability, both delay-dependent and delay-independent. Moreover, we formulate an explicit bound on the exponential decay rate of the state evolution, as a function of the maximum delay. We then show that the aforementioned stability conditions also prove input-to-state stability. The stability conditions consist of simple linear inequalities, albeit infinite-many due to the time-varying nature of the system. To overcome the computational burden, we also introduce a simple relaxation that allows to check the stability with a finite test, at the expense of conservatism. Finally, leveraging comparison systems and results from the theory of non-negative matrices, we generalize all the aforementioned results to systems with no sign constraint, for which we still provide stability conditions by means of linear inequalities and guaranteed convergence rate. Some consequences and a comparative example are provided for the well investigated special case of systems with constant matrices and time-varying delays.

Interval approximation method for stability analysis of time-delay systems

This paper investigates the stability issues of linear systems with a sinusoidal delay, utilizing a refined switching allowable delay set (ADS) derived from the delay‐splitting technique (DST). The delay function is divided into multiple segments and defines their respective value ranges using the DST. By accurately calculating the delay derivatives at each segment point, a refined ADS with a tighter boundary condition is established. Based on this ADS, a stability criterion specifically for linear systems with sinusoidal delays is introduced, demonstrating a significant reduction in conservativeness. Additionally, an improved DST‐based Lyapunov–Krasovskii functional (LKF) is proposed. Compared to similar LKFs reported in the literature, our approach imposes more relaxed constraints, further reducing the conservativeness of the results. Finally, the validity and applicability of our proposed approaches are verified through two extensively researched numerical examples.

Stability analysis of linear delayed systems based on an allowable delay set partitioning approach

In this paper, the stability analysis of linear systems with time-varying delays is studied. A novel Lyapunov method is presented, in which positive definiteness of the matrices in common Lyapunov functionals is relaxed by adding what is referred to as a zero-integral functional (ZIF). A general form of auxiliary polynomial-based functionals that contains such ZIF is given. Choosing polynomials of different order as well as exploring double-delay-product (DDP) terms, novel Lyapunov functionals are constructed, which contribute to a set of improved stability conditions expressed in terms of linear matrix inequalities. Finally, numerical examples are provided to corroborate the merits of the proposed method relative to a number of existing methods, and in particular, the effectiveness of the proposed ZIFs and DDP terms in reducing the conservatism of stability conditions.

Polynomials-based integral inequality for stability analysis of linear systems with time-varying delays