Linear Matrix Inequality Feasibility Tests Research Articles

An exact LMI condition for the strong delay‐independent stability analysis of neutral delay systems

SummaryThis paper concentrates on strong delay‐independent stability of neutral linear time‐invariant delay systems with multiple commensurate time delays. The stability analysis of linear neutral systems is complicated by the need to locate the roots of a transcendental characteristic equation and to take into account the global hyperbolicity of an associated difference system. In this paper, we propose a convex necessary and sufficient condition for testing strong delay‐independent stability. This result mainly follows from Kronecker sum properties and the Kalman‐Yakubovich‐Popov lemma, which allows us to present the main result in terms of a single linear matrix inequality feasibility test. The paper is closed by showing numerical examples that illustrate the applicability and effectiveness of the proposed method.

Affine Parameter-Dependent Lyapunov Functions for LPV Systems With Affine Dependence

This paper deals with the certification problem for robust quadratic stability, robust state convergence, and robust quadratic performance of linear systems that exhibit bounded rates of variation in their parameters. We consider both continuous-time (CT) and discrete-time (DT) parameter-varying systems. In this paper, we provide a uniform method for this certification problem in both cases and we show that, contrary to what was claimed previously, the DT case requires a significantly different treatment compared to the existing CT results. In the established uniform approach, quadratic Lyapunov functions, that are affine in the parameter, are used to certify robust stability, robust convergence rates, and robust performance in terms of linear matrix inequality feasibility tests. To exemplify the procedure, we solve the certification problem for $\mathscr{L}_2$-gain performance both in the CT and the DT cases. A numerical example is given to show that the proposed approach is less conservative than a method with slack variables.

Control With Communications Constraints: Measuring the Instability in Parametric Linear Systems

This paper investigates the instability measure of linear systems defined as the sum of the unstable eigenvalues in the continuous-time case and the product of the unstable eigenvalues in the discrete-time case. The problem consists of determining the largest instability measure in systems depending polynomially on parameters constrained in a semialgebraic set. It is shown that upper bounds of the sought measure can be established via linear matrix inequality feasibility tests. Moreover, a priori and a posteriori conditions for establishing nonconservatism are proposed. Finally, two special cases of the proposed methodology are investigated-the first one concerns systems with a single parameter, and the second one concerns the determination of the largest spectral abscissa and radius. Three applications in control with communications constraints are discussed.

New stabilisation schemes for discrete delay systems with uncertain non-linear perturbations

New ℋ∞ controller design schemes are provided for a class of discrete-time systems with uncertain non-linear perturbations. The class includes both systems with time-varying delays and systems without delay. One design scheme is generated by state-feedback and the other scheme is based on proportional–summation–difference (PSD) feedback. An appropriate Lyapunov–Krasovskii functional (LKF) is constructed and a new parametrised characterisation is established in terms of feasibility-testing of linear matrix inequalities (LMIs). Numerical examples are given to illustrate the theoretical developments.

Linear hybrid systems with time-varying delays: H<SUB align=right>∞ stabilisation schemes

In this paper, we provide new stabilisation schemes for a class of linear Hybrid Time-Delay (HTD) systems under arbitrary switching. These schemes are delay-independent and delay-dependent H∞ stabilisation based on Proportional-Integral-Derivative (PID) feedback strategy. By adopting a selective Lyapunov-Krasovskii Functional (LKF), new criteria are constructed in a systematic way in terms of feasibility-testing of Linear Matrix Inequalities (LMIs). When the time-delay is a continuous bounded function, we derive the solution for nominal and polytopic models as well identifying several existing results as special cases. In case the time-delay is a differentiable time-varying function satisfying some bounding relations, we establish new parametrised LMI characterisations for PID feedback stabilisation. Numerical examples are provided to illustrate the theoretical developments.

Robust Analysis of LFR Systems Through Homogeneous Polynomial Lyapunov Functions

In this note, the use of homogeneous polynomial Lyapunov functions (HPLFs) for robust stability analysis of linear systems subject to time-varying parametric uncertainty, affecting rationally the state space matrix, is investigated. Sufficient conditions based on linear matrix inequalities feasibility tests are derived for the existence of HPLFs, which ensure robust stability when the uncertain parameter vector is restricted to lie in a convex polytope. It is shown that HPLFs lead to results which are less conservative than those obtainable via quadratic Lyapunov functions.

An LMI condition for the robust stability of uncertain continuous-time linear systems

A new sufficient condition for the robust stability of continuous-time uncertain linear systems with convex bounded uncertainties is proposed in this note. The results are based on linear matrix inequalities (LMIs) formulated at the vertices of the uncertainty polytope, which provide a parameter dependent Lyapunov function that assures the stability of any matrix inside the uncertainty domain. With the aid of numerical procedures based on unidimensional search and the LMIs feasibility tests, a simple and constructive way to compute robust stability domains can be established.