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Journal ArticleDOI

Notes on Stability of Time-Delay Systems: Bounding Inequalities and Augmented Lyapunov-Krasovskii Functionals

TL;DR: It is proved that, when a simple LKF is applied, the stability criteria obtained by the Wirtinger-based inequality and the Jensen inequality are equivalent, which means that the tighter inequality does not always lead to a less conservative criterion.
Abstract: The bounding inequalities and the Lyapunov-Krasovskii functionals (LKFs) are important for the stability analysis of time-delay systems. Much attention has been paid to develop tighter inequalities for improving stability criteria, while the contribution of the LKFs has not been considered when discussing the relationship between the tightness of inequalities and the conservatism of criteria. This note is concerned with this issue. Firstly, it is proved that, when a simple LKF is applied, the stability criteria obtained by the Wirtinger-based inequality and the Jensen inequality are equivalent although the Wirtinger-based inequality is tighter. It means that the tighter inequality does not always lead to a less conservative criterion. Secondly, it is found that a suitable augmented LKF with necessary integral vectors in its derivative is required to achieve the advantage of the Wirtinger-based inequality. Based on this observation, two delay-product-type terms are introduced into the LKF to establish new stability criteria. Finally, a numerical example is given to verify the equivalence statements and to show the benefit of the proposed criteria.
Citations
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Journal ArticleDOI
TL;DR: A comprehensive security understanding of the SGs framework, attacks scenarios, detection/protection methods, estimation and control strategies from both communication and control viewpoints are addressed.
Abstract: Smart grids (SGs), which can be classified into a class of networked distributed control systems, are designed to deliver electricity from various plants through a communication network to serve individual consumers. Due to the complexity of environments, the distribution of the spatial locations and vulnerability of the communication networks, cyber security emerges to be a critical issue because millions of electronic devices are interconnected via communication networks throughout critical power facilities. This paper addresses a comprehensive security understanding of the SGs framework, attacks scenarios, detection/protection methods, estimation and control strategies from both communication and control viewpoints. Also, some potential challenges and solution approaches are discussed to deal with the threat issues of SGs. At last, some conclusions and highlight future research directions are presented.

235 citations


Cites background from "Notes on Stability of Time-Delay Sy..."

  • ...For examples, besides time delay, packet dropouts, or bandwidth limitation of their own challenges for communication networks [12], a security transmission manner is required so as to avoid malicious jamming or tamper [13]; besides the accuracy or intelligence requirements, fabricating smart meter readings and manipulating energy costs will impose extra limitations for AMIs which are wildly used in SGs [14]....

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Journal ArticleDOI
TL;DR: In this article, the authors provide an overview and in-depth analysis of recent advances in stability of linear systems with time-varying delays, including stability criteria for three cases of a time varying delay.
Abstract: This study provides an overview and in-depth analysis of recent advances in stability of linear systems with time-varying delays. First, recent developments of a delay convex analysis approach, a reciprocally convex approach and the construction of Lyapunov–Krasovskii functionals are reviewed insightfully. Second, in-depth analysis of the Bessel–Legendre inequality and some affine integral inequalities is made, and recent stability results are also summarised, including stability criteria for three cases of a time-varying delay, where information on the bounds of the time-varying delay and its derivative is totally known, partly known and completely unknown, respectively. Third, a number of stability criteria are developed for the above three cases of the time-varying delay by employing canonical Bessel–Legendre inequalities, together with augmented Lyapunov–Krasovskii functionals. It is shown through numerical examples that these stability criteria outperform some existing results. Finally, several challenging issues are pointed out to direct the near future research.

210 citations

Journal ArticleDOI
TL;DR: A generalized free-matrix-based integral inequality (GFMBII) is presented that overcomes the drawback that the Bessel–Legendre inequality is inconvenient to cope with a time-varying delay system as the resultant bound contains a reciprocal convexity.

184 citations

Journal ArticleDOI
TL;DR: A parameter-adjustable-based lemma is developed, which contains the lemma popularly used in literature as a special case and has potential to reduce the conservatism without requiring extra decision variables.

170 citations

Journal ArticleDOI
TL;DR: It is proved that these existing inequalities can be captured as particular cases of Moon et al.'s inequality and found strong links not only with the most recent and efficient matrix inequalities such as the reciprocally convex combination lemma and also its relaxed version but also with some previous inequalities.

148 citations

References
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Journal ArticleDOI
TL;DR: This paper suggests the lower bound lemma for such a combination, which achieves performance behavior identical to approaches based on the integral inequality lemma but with much less decision variables, comparable to thosebased on the Jensen inequalityLemma.

2,248 citations


"Notes on Stability of Time-Delay Sy..." refers background or methods in this paper

  • ...Lemma 2: ([7], [27]) For given vectors β1 and β2 , scalar α in the interval (0, 1), symmetric positive definite matrix R ∈ Rn×n and any matrix X ∈ Rn×n satisfying [ R X ∗ R ] ≥ 0, the following inequality holds...

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  • ...(1) Proof of C1: when Φ1 ≥ 0 holds for any matrix S, using JI (3) and (5) to estimate the integral term in (9) yields [27]...

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Journal ArticleDOI
TL;DR: An alternative inequality based on the Fourier Theory, more precisely on the Wirtinger inequalities is proposed and it is shown that this resulting inequality encompasses the Jensen one and also leads to tractable LMI conditions.

1,791 citations


"Notes on Stability of Time-Delay Sy..." refers background or methods in this paper

  • ...(2) Proof of C2: when Ψ1 ≥ 0 holds for any matrix U , using WBI (4) and (5) to estimate the integral term in (10) yields [7]...

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  • ...By comparing the proof of Theorem 1 and Theorem 7 of [7], the key difference is that the LKF used in [7] includes an augmented non-integral term, which activates the advantage of the WBI....

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  • ...An alternative type of method is to directly estimate the integral term via bounding inequalities, among which Jensen inequality (JI) [15] and Wirtinger-based inequality (WBI) [7] are frequently applied....

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  • ...Lemma 1: (Jensen Inequality [15] and Wirtinger-Based Inequality [7]): For given symmetric positive definite matrix R ∈ Rn×n , scalars a and b satisfying a b, and vector ω : [a, b] → Rn such that the integrations concerned are well defined, the following inequalities hold (b − a) ∫ b a ωT (s)Rω(s)ds ≥ χT1 Rχ1 (3) (b − a) ∫ b a ωT (s)Rω(s)ds ≥ χT1 Rχ1 + 3χT2 Rχ2 (4) where χ1 = ∫ b a ω(s)ds and χ2 =χ1 − 2b−a ∫ b a ∫ s a ω(u)duds....

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  • ...Lemma 2: ([7], [27]) For given vectors β1 and β2 , scalar α in the interval (0, 1), symmetric positive definite matrix R ∈ Rn×n and any matrix X ∈ Rn×n satisfying [ R X ∗ R ] ≥ 0, the following inequality holds...

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Proceedings ArticleDOI
12 Dec 2000
TL;DR: In this paper, an integral inequality is derived, and applied to the stability problem of time-delay systems using discretized Lyapunov functional formulation, and a simpler stability criterion is derived.
Abstract: An integral inequality is derived, and applied to the stability problem of time-delay systems using discretized Lyapunov functional formulation. As the result, a simpler stability criterion is derived.

1,521 citations


"Notes on Stability of Time-Delay Sy..." refers background or methods in this paper

  • ...Lemma 1: (Jensen Inequality [15] and Wirtinger-Based Inequality [7]): For given symmetric positive definite matrix R ∈ Rn×n , scalars a and b satisfying a < b, and vector ω : [a, b] → Rn such that the integrations concerned are well defined, the following inequalities hold...

    [...]

  • ...Lemma 1: (Jensen Inequality [15] and Wirtinger-Based Inequality [7]): For given symmetric positive definite matrix R ∈ Rn×n , scalars a and b satisfying a b, and vector ω : [a, b] → Rn such that the integrations concerned are well defined, the following inequalities hold (b − a) ∫ b a ωT (s)Rω(s)ds ≥ χT1 Rχ1 (3) (b − a) ∫ b a ωT (s)Rω(s)ds ≥ χT1 Rχ1 + 3χT2 Rχ2 (4) where χ1 = ∫ b a ω(s)ds and χ2 =χ1 − 2b−a ∫ b a ∫ s a ω(u)duds....

    [...]

  • ...An alternative type of method is to directly estimate the integral term via bounding inequalities, among which Jensen inequality (JI) [15] and Wirtinger-based inequality (WBI) [7] are frequently applied....

    [...]

Journal ArticleDOI
TL;DR: Some new delay-dependent stability criteria are devised by taking the relationship between the terms in the Leibniz-Newton formula into account, which are less conservative than existing ones.

1,069 citations


"Notes on Stability of Time-Delay Sy..." refers methods in this paper

  • ...Model transformations [8]–[10] and various free-weighting-matrix approach [11]–[14] are applied to estimate the integral term in the early research....

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Journal ArticleDOI
TL;DR: The present results may improve the existing ones due to a method to estimate the upper bound of the derivative of Lyapunov functional without ignoring some useful terms and the introduction of additional terms into the proposed Lyap unov functional, which take into account the range of delay.

899 citations