Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2012, Article ID 830154, 25 pages doi:10.1155/2012/830154 Research Article Robust Finite-Time H∞ Control for Impulsive Switched Nonlinear Systems with State Delay Jian Guo, Chao Liu, and Zhengrong Xiang School of Automation, Nanjing University of Science and Technology, Nanjing 210094, China Correspondence should be addressed to Zhengrong Xiang, xiangzr@mail.njust.edu.cn Received 20 June 2012; Revised 9 September 2012; Accepted 10 September 2012 Academic Editor: Zidong Wang Copyright q 2012 Jian Guo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper investigates robust finite-time H∞ control for a class of impulsive switched nonlinear systems with time-delay. Firstly, using piecewise Lyapunov function, sufficient conditions ensuring finite-time boundedness of the impulsive switched system are derived. Then, finite-time H∞ performance analysis for impulsive switched systems is developed, and a robust finite-time H∞ state feedback controller is proposed to guarantee that the resulting closed-loop system is finite-time bounded with H∞ disturbance attenuation. All the results are given in terms of linear matrix inequalities LMIs. Finally, two numerical examples are provided to show the effectiveness of the proposed method. 1. Introduction A switched system is a hybrid dynamical system consisting of a family of continuous-time or discrete-time subsystems and a switching law that orchestrates the switching between them 1. In the last decades, in the stability analysis and stabilization for switched systems, lots of valuable results are established see 2–5. Most recently, on the basis of Lyapunov functions and other analysis tools, the stability problem of linear and nonlinear switched systems with time-delay has been further investigated see 6–15, and lots of valuable results are established for H∞ control problems see 16–22. It is well known that impulsive dynamical behaviors inevitably exist in some practical systems like physical, biological, engineering, and information science systems due to abrupt changes at certain instants during the dynamical process. Although hybrid system and switched system are important models for dealing with complex real systems, there is little work concerned with the above impulsive phenomena. Such a phenomenon can be modeled 2 Mathematical Problems in Engineering as an impulsive switched system, it is characteristic that their states change during the switching because of the occurrence of impulses 23. In recent years, the impulsive switched systems have drawn more and more attention and many useful conclusions have been obtained. Multiple Krasovskii-Lyapunov function approach is employed to study the problem of ISS stability of a class of impulsive switched systems with time-delay in 24. By the Lyapunov-Razumikhin technique, a delayindependent criterion of the exponential stability is established on the minimum dwell time in 25. The problem of robust H∞ stabilization of nonlinear impulsive switched system with time-delays is studied in 23. Usually, the stability of a system is defined over an infinite-time interval. But in many practical systems, we focus on the dynamical behavior of a system over a fixed finite-time interval. Based on this, finite-time stability is first proposed by Dorato in 1961 26. Compared with the classical Lyapunov stability, finite-time stability is proposed for the study of the transient performance of the system, which is a totally different concept. The so-called finitetime stability means the boundedness of the state of a system over a fixed finite-time interval. Finite-time stability problems can be found in 27–32. The finite-time stability of linear impulsive systems is analyzed in 33, the finite-time stability and stabilization of impulsive dynamic systems are carried out in 34–36. The finite-time stability and stabilization of switched systems are investigated in 37. Recently, robust finite-time control of switched systems is studied in 38, 39. However, to the best of our knowledge, there are very few results on finite-time boundedness and robust H∞ control of the impulsive switched systems, which motivates the present study. The paper is organized as follows. In Section 2, problem formulation and some necessary lemmas are given. In Section 3, based on the dwell time approach, finite-time boundedness and finite-time H∞ performance for switched impulsive systems are addressed, and sufficient conditions for the existence of a robust finite-time H∞ state feedback controller are proposed in terms of a set of matrix inequalities. Numerical examples are provided to show the effectiveness of the proposed approach in Section 4. Concluding remarks are given in Section 5. Notations. The notations used in this paper are standard. The notation P > 0 means that P is a real positive definite matrix; diag{· · · } stands for a block-diagonal matrix; λmax P and λ P denote the maximum and minimum eigenvalues of matrix P , respectively; xt min ∞ 2 xT txt and xt2 0 xt dt1/2 . 2. Problem Formulation and Preliminaries Consider the following impulsive switched system: σt xt A dσt xt − h B1σt u1 t fσt xt B2σt wt, ẋt A Δx Eσt xt u2 t, t tk , k 1, 2, 3, . . . t/ tk 2.1a 2.1b zt Cσt xt Dσt u1 t, 2.1c xt ϕt, 2.1d t ∈ t0 − h, t0 , Mathematical Problems in Engineering 3 where xt ∈ Rn is the state vector, zt ∈ Rr is the controlled output, wt ∈ Rp is the tk is the switched control input, disturbance input which belongs to L2 0, ∞, u1 t ∈ Rm , t / tk , k u2 tk ∈ Rn is the impulsive control input at tk , on the other hand, u2 t 0, t / 1, 2, 3, . . .. σt : t0 , ∞ → N {1, 2, . . . , N} is a switching signal. t ∈ tk , tk1 , σt ik , ik ∈ N, k 0, 1, 2, 3, . . .. Δxt xt − xt− , xt limh → 0 xt h, xt xt− limh → 0 xt − h. tk , k 0, 1, 2, 3, . . . are the impulsive jumping points or switching points. t0 is the initial time, t0 < t1 < · · · < tk < · · · , and limk → ∞ tk ∞. h > 0 is the time-delay which is a positive constant. fi · : Rn → Rn , i ∈ N is nonlinear vector-valued function. i, A di , B1i , i ∈ N are ϕt, t ∈ t0 − h, t0 is a continuous vector-valued initial function. A uncertain real-valued matrices with appropriate dimensions, B2i , Ei , Ci , Di , i ∈ N are known real constant matrices with appropriate dimensions. i, A di , B1i are uncertain real-valued matrices with Assumption 2.1. For each i ∈ N, A appropriate dimensions. We assume that the uncertainties are of the form di Adi ΔAdi , i Ai ΔAi , A B1i B1i ΔB1i , A ΔAi ΔAdi ΔB1i Hi Fi t EAi EAdi EBi , 2.2a 2.2b where Ai , Adi , B1i , Hi , EAi , EAdi , and EBi are known real-valued constant matrices with appropriate dimensions, Fi t is the uncertain matrix satisfying 2.3 FiT tFi t ≤ I. Assumption 2.2. For each i ∈ N, nonlinear vector-valued function fi satisfies Lipschitz condition fi xt ≤ Ui xt, 2.4 where Ui is the Lipschitz constant matrix. Assumption 2.3. For a given time constant Tf > t0 , the external disturbance wt satisfies Tf 2.5 wT twtdt ≤ d2 . 0 Assumption 2.4. For system 2.1a–2.1d, the impulsive jump matrices Ei satisfy that I Ei are invertible. Definition 2.5 see 32. For a given time constant Tf > t0 , impulsive switched system 2.1a, 2.1b, 2.1c and 2.1d with u1 t ≡ 0, u2 t ≡ 0, and wt ≡ 0, is said to be finite-time stable with respect to c12 , c22 , Tf , R, σt if the following inequality holds: sup xT τRxτ ≤ c12 ⇒ xT tRxt < c22 , t0 −h≤τ≤t0 t ∈ t0 , T f , where c2 > c1 > 0, R is a positive definite matrix, and σt is a switching signal. 2.6 4 Mathematical Problems in Engineering Remark 2.6. Equation 2.6 stands for the boundedness of the state of a system over a fixed finite-time interval t0 , Tf , when the initial state is bounded. Definition 2.7 see 40. For a given time constant Tf , impulsive switched system 2.1a– 2.1d with u1 t ≡ 0, u2 t ≡ 0, and wt satisfying 2.5, is said to be finite-time bounded with respect to c12 , c22 , Tf , d2 , R, σt if the condition 2.6 holds, where c2 > c1 > 0, R is a positive definite matrix and σt is a switching signal. Definition 2.8. For any T2 > T1 > 0, let Nσt T1 , T2 denote the switching number of σt on an interval T1 , T2 . If Nσt T1 , T2 ≤ N0 T2 − T1 /τa holds for given N0 ≥ 0, τa > 0, then the constant τa is called the average dwell time. In this paper we let N0 0. Definition 2.9. For a given time constant Tf , impulsive switched system 2.1a–2.1d with u1 t ≡ 0, u2 t ≡ 0 is said to have finite-time H∞ performance with respect to 0, c22 , Tf , d2 , γ, R, σt if the system is finite-time bounded and the following inequality holds: zt2 ≤ γwt2 , ∀wt ∈ L2 0, ∞, 2.7 where c2 > 0, γ > 0, R is a positive definite matrix and σtis a switching signal. Definition 2.10. For a given time constant Tf , impulsive switched system 2.1a–2.1d is said to be robust finite-time stabilization with H∞ disturbance attenuation level γ, if there tk and an impulsive controller u2 tk exists a switched controller u1 t Kσt xt, t / K σt xtk , t tk , where t ∈ t0 , Tf such that i the corresponding closed-loop system is finite-time bounded with respect to 0, c22 , Tf , d2 , R, σt; ii under zero initial condition, inequality 2.7 holds for any wt satisfying 2.5. Lemma 2.11. Let U, V , W, and X be real matrices of appropriate dimensions with X satisfying X X T , then for all V T V ≤ I, X UV W W T V T UT < 0, 2.8 if and only if there exists a scalar ε > 0 such that X εUUT ε−1 W T W < 0. 2.9 Mathematical Problems in Engineering 5 3. Main Results 3.1. Finite-Time Boundedness Analysis In this subsection, we focus on the finite-time boundedness of the following impulsive switched system: ẋt Aσt xt Adσt xt − h fσt xt B2σt wt, Δx Eσt xt, t tk , xt ϕt, t/ tk k 1, 2, 3, . . . t ∈ t0 − h, t0 . 3.1a 3.1b 3.1c Before proceeding to Lemma 3.2, we first introduce a function vt. For given positive definite matrices Qik , ik ∈ N, by Assumption 2.4, there exists a real number ρik ≥ 1, ρ∗ max{ρik , ik ∈ N} such that Qik−1 ≤ ρik I Eik−1 T Qik I Eik−1 . 3.2 Furthermore, we define the following function vk t ρik − ρik − 1 , t − tk 2 2 tk1 − tk t ∈ tk , tk1 . 3.3 Finally, a piecewise continuous function vt is as follows: vt vk t, t ∈ tk , tk1 . 3.4 Consider the function vt, for each interval tk , tk1 , vtk ρik , vtk1 1, and vt is monotonically nonincreasing and bounded function, vtk1 ≤ vt ≤ vtk . Remark 3.1. Note that the previous works require the condition Qik−1 ≤ I Eik−1 T Qik I Eik−1 see 23, 41, which can be obtained by setting ρik 1 in 3.2. Thus, the proposed approach may provide more relaxed conditions. Lemma 3.2. Consider the following Lyapunov functional candidate: V t xT tPσt xt t vsxT seαt−s Qσs xsds 3.5 t−h for system 3.1a, 3.1b, and 3.1c, where Pi and Qi , i ∈ N are symmetric positive definite matrices with appropriate dimensions. 6 Mathematical Problems in Engineering The following inequality is derived: V̇ t ≤ 2x tPik ẋt α T t vsxT seαt−s Qσs xsds t−h vtxT tQik xt − vt − hxT t − hQik−m xt − heαh t ∈ tk , tk1 , t − h ∈ tk−m , tk−m1 , 3.6 m ∈ {0, 1, 2, 3, . . .}. Proof. i When tk h ≥ tk1 , V t x tPσt xt T t vsxT seαt−s Qσs xsds t−h xT tPik xt tk−m2 tk−m1 t−h vsx se T tk−m1 V̇ t 2xT tPik ẋt α vsxT seαt−s Qik−m xsds αt−s t Qik−m1 xsds · · · t tk vsxT seαt−s Qik xsds, vsxT seαt−s Qσs xsds t−h vtk−m1 x tk−m1 eαt−tk−m1 Qik−m xtk−m1 T − vt − hxT t − heαh Qik−m xt − h vtk−m2 xT tk−m2 eαt−tk−m2 Qik−m1 xtk−m2 − v tk−m1 xT tk−m1 eαt−tk−m1 Qik−m1 x tk−m1 · · · vtk xT tk eαt−tk Qik−1 xtk − v tk−1 xT tk−1 eαt−tk Qik−1 x tk−1 vtxT tQik xt − v tk xT tk eαt−tk Qik x tk , t T V̇ t 2x tPik ẋt α vsxT seαt−s Qσs xsds t−h vtxT tQik xt − vt − hxT t − heαh Qik−m xt − h xT tk−m1 eαt−tk−m1 Qik−m − ρik−m1 I Eik−m T Qik−m1 I Eik−m xtk−m1 . . . xT tk eαt−tk Qik−1 − ρik I Eik−1 T Qik I Eik−1 xtk . 3.7 Mathematical Problems in Engineering 7 From 3.2, we can obtain that Qik−m − ρik−m1 I Eik−m T Qik−m1 I Eik−m ≤ 0 .. . 3.8 Qik−1 − ρik I Eik−1 T Qik I Eik−1 ≤ 0. Combining 3.7 and 3.8, 3.6 is obtained. ii When tk h < tk1 , 1 t ∈ tk , tk h, the proof is similar to the proof line in the situation i. 2 t ∈ tk h, tk1 , V t xT tPσt xt xT tPik xt t t vsxT seαt−s Qσs xsds t−h t−h 3.9 vsxT seαt−s Qik xsds. The proof for this situation is omitted. The proof is completed. Lemma 3.3. Consider the following Lyapunov function: V t xT tPσt xt t vsxT seαt−s Qσs xsds 3.10 t−h for system 3.1a, 3.1b, and 3.1c, where Pi and Qi , i ∈ {1, 2, . . . , N} are symmetric positive definite matrices with appropriate dimensions. Under the condition ⎤ ⎡ αh ∗ EiT −e ρ Pj I EjT ⎥ ⎢ ∗ −Pi−1 0 ⎦ < 0, ⎣ −1 −1 −αh ∗ Qi ∗ ∗ −e ρ ∀i, j ∈ N, 3.11 we have V tk < eαh ρ∗ V tk , where ρ∗ max{ρik , ik ∈ N}. 3.12 8 Mathematical Problems in Engineering Proof. Without loss of generality, let σtk i, σtk j. Then, we have V tk xT tk Pσtk x tk t k tk −h vsxT seαtk −s Qσs xsds ≤ x tk Pσtk x tk eαh ρ∗ T t k tk −h xT sQσs xsds T ≤ x tk I Ej Pi I Ej xtk eαh ρ∗ xT tk EjT Qi Ej xtk T αh ∗ e ρ tk tk −h 3.13 vsxT seαtk −s Qσs xsds, V tk x tk Pj xtk T tk tk −h vsxT seαtk −s Qσs xsds. 3.14 Combining 3.13 with 3.14, we have T V tk − eαh ρ∗ V tk ≤ xT tk I Ej Pi I Ej xtk eαh ρ∗ xT tk EjT Qi Ej xtk − eαh ρ∗ xT tk Pj xtk 3.15 xT tk Σij xtk , where T I Ej Pi I Ej eαh ρ∗ EjT Qi Ej − eαh ρ∗ Pj . ij 3.16 Using Schur complement, 3.11 is equivalent to Σij < 0 or The proof is completed. V tk − eαh ρ∗ V tk < 0. 3.17 Mathematical Problems in Engineering 9 i R−1/2 Qi R−1/2 , For all i ∈ Theorem 3.4. R is a positive definite matrix. Let Pi R−1/2 Pi R−1/2 , Q ∗ N, if there exist positive scalars ρi ≥ 1, i ∈ N, ρ max{ρi , i ∈ N}, α, λ1 , λ2 , λ3 and symmetric positive matrices Pi , Pj , Qi , Ti , i, j ∈ N such that 1 i ≤ 0, j I Ei −T − Q I Ei −1 Q ρ∗ ∀i, j ∈ N ⎡ ⎤ i B2i Pi ATi Ai Pi − αPi I Adi Q Pi ⎢ ⎥ j 0 ⎢ ⎥ ∗ −eαh Q 0 ⎢ ⎥ < 0, ⎢ ⎥ 0 ∗ ∗ −Ti ⎦ ⎣ T ∗ −1 ∗ ∗ ∗ − ρ Qi Uik Uik ⎡ ⎤ −eαh ρ∗ Pj Pj I EjT Pj EjT ⎢ ⎥ ⎢ ⎥ < 0, ∗ −Pi 0 ⎣ ∗ −1 ⎦ −αh i ∗ ∗ −e Q ρ 3.18 ∀i, j ∈ N ∀i, j ∈ N i , Ti < λ3 I, ∀i ∈ N λ1 R−1 < Pi < R−1 , λ2 R−1 < Q ⎤ ⎡ 2 −αTf d2 λ3 c1 c1 −c2 e ⎥ ⎢ ∗ −λ1 0 ⎥<0 ⎢ ⎣ 1 −αh ⎦ ∗ ∗ − ∗ e λ2 ρ h 3.19 3.20 3.21 3.22 hold, under the average dwell time scheme τa > τa∗ Tf αh ln ρ∗ 2 −αT , ln c2 e f − ln 1/λ1 hρ∗ eαh /λ2 c12 d2 λ3 3.23 system 3.1a–3.1c is finite-time bounded with respect to c12 , c22 , Tf , d2 , R, σt. Proof. Assuming that when t ∈ tk , tk1 , σt ik , ik ∈ N, k 0, 1, 2, 3, . . .. Choose the following Lyapunov functional candidate: −1 V t x tPσt xt T t t−h −1 xsds. vsxT seαt−s Q σs 3.24 10 Mathematical Problems in Engineering When t ∈ tk , tk1 , according to 3.18 and Lemma 3.2, we have V̇ t ≤ 2xT tPi−1 ẋt α k vtx T t−h −1 xt tQ ik ẋt α V̇ xt − αV xt − w tTik wt ≤ 2x tPi−1 k T t T −1 xsds vsxT seαt−s Q σs −1 xt − heαh , − vt − hxT t − hQ ik−m t t−h −1 xsds vsxT seαt−s Q σs −1 xt − vt − hxT t − hQ −1 xt − heαh vtxT tQ ik ik−m − αx tPi−1 xt − α k T t t−h −1 xsds vsxT seαt−s Q σs − wT tTik wt −1 xt ≤ 2xT tPi−1 ẋt ρ∗ xT tQ ik k −1 xt − heαh − αxT tP −1 xt − xT t − hQ ik−m ik − wT tTik wt. 3.25 According to 3.1a–3.1c, and 3.25, Assumption 2.2, and the fallowing inequality: 2xT tPi−1 fxt ≤ fiTk xtfik xt xT tPi−1 xt Pi−1 k k k ≤ xT tUiTk Uik xt xT tPi−1 xt, Pi−1 k k 3.26 we have V̇ xt − αV xt − wT tTik wt ≤ X T tΞk Xt, 3.27 where X T t xT txT t − hwT t, ⎤ ⎡ Adik Pi−1 B2ik Δk Pi−1 k k ⎥ ⎢ −1 Ξk ⎣ ∗ −eαh Q 0 ⎦, ik−m ∗ ∗ −Tik 3.28 −1 − αP −1 UT Uik P −1 P −1 . Δk ATik Pi−1 Pi−1 Aik ρ∗ Q ik ik ik ik ik k k Using Schur complement, we obtain from 3.19 that ⎤ ⎡ Oi Pi−1 Adi Pi−1 B2i ⎥ ⎢ −1 0 ⎦ < 0, ⎣ ∗ −eαh Q j ∗ ∗ −Ti 3.29 Mathematical Problems in Engineering 11 where −1 − αP −1 UT Ui P −1 P −1 . Oi ATi Pi−1 Pi−1 Ai ρ∗ Q i i i i i 3.30 Noticing that the above inequality holds for all i, j ∈ N, then we have Ξk < 0 for ik , ik−1 ∈ N. Thus, 3.31 V̇ xt − αV xt − wT tTik wt < 0. When t ∈ tk , tk1 , according to Lemma 3.3, we can obtain 3.12 from condition 3.20. Combining 3.31 and 3.12, we can obtain that V t < e <e αt−tk V tk t eαt−s wT sTik wsds tk αt−tk αh ∗ e ρ V tk t tk <e αt−tk αh ∗ e ρ e t tk αtk −tk−1 eαt−s wT sTik wsds V tk−1 tk e αtk −s tk−1 w sTik−1 wsds T eαt−s wT sTik wsds < ··· <e αt−t0 αh ∗ e ρ Nσ t0 ,t αh ∗ V t0 e ρ Nσ t0 ,t t1 eαt−s wT sTi0 wsds t0 αh ∗ e ρ Nσ t1 ,t t2 · · · eαh ρ∗ tk tk−1 eαt−t0 eαh ρ∗ e αt−s w sTi1 wsds t1 eαt−s wT sTik−1 wsds Nσ t0 ,t 3.32 T V t0 t t tk eαt−s eαh ρ∗ eαt−s wT sTik wsds Nσ s,t t0 <e <e αt αTf αh ∗ e ρ Nσ t0 ,t αh ∗ e ρ αh ∗ V t0 e ρ Nσ t0 ,t Nσ t0 ,t e αt t t0 V t0 Tf t0 wT sTik wsds w sTik wsds T Nσ t0 ,t V t0 λmax Tik d2 . < eαTf eαh ρ∗ wT sTik wsds 12 Mathematical Problems in Engineering Noticing that Nσ t0 , Tf < Tf /τa and according to 3.21, we have T /τ V t < eααh/τa Tf ρ∗ f α V t0 λ3 d2 , V t ≥ xT tPi−1 xt xT tR1/2 Pi−1 R1/2 xt k k xT tRxt ≥ λmin Pi−1 k 3.33 1 xT tRxt. λmax Pik Because λ1 R−1 < Pi < R−1 , we have 3.34 V t > xT tRxt. According to the Lyapunov function that we have chosen, we have V t0 xT t0 Pi−1 xt0 t0 −1 xsds vsxT se−αt0 −s Q i t0 −h ≤ max λmax Pi−1 xT t0 Rxt0 i∈N heαh ρ∗ max λmax Qi−1 sup xT θRxθ 3.35 t0 −h≤θ≤t0 i∈N ⎛ ⎞ ∗ αh he ρ 1 ⎠ sup xT θRxθ. ≤⎝ min λmin Pi min λmin Qi t0 −h≤θ≤t0 i∈N i∈N According to 3.21, the following inequality is derived: V t0 < ρ∗ heαh 1 λ1 λ2 3.36 c12 . Combining 3.33, 3.34, and 3.36, we can obtain that x tRxt < V t < e T ααh/τa Tf ∗ Tf /τα ρ ρ∗ heαh 1 λ1 λ2 c12 λ3 d . 2 3.37 Using Schur complement, 3.22 is equivalent to ρ∗ heαh 1 λ1 λ2 From 3.38, we can obtain that τa > 0. c12 λ3 d2 < c22 e−αTf . 3.38 Mathematical Problems in Engineering 13 Substituting 3.23 into 3.37 leads to 3.39 xT tRxt < c22 . Thus, system 3.1a–3.1c is finite-time bounded with respect to c12 , c22 , Tf , d2 , R, σt. The proof is completed. i Corollary 3.5. R is a positive definite matrix, let wt ≡ 0, Pi R−1/2 Pi R−1/2 , Q −1/2 −1/2 ∗ Qi R for all i ∈ N. If there exist positive scalars ρi ≥ 1, i ∈ N, ρ max{ρi , i ∈ N}, R α, λ1 , λ2 and symmetric positive matrices Pi , Pj , Qi for all i, j ∈ N with appropriate dimensions such that 1 i ≤ 0, j I Ei −T − Q I Ei −1 Q ρ∗ ∀i, j ∈ N ⎡ T ⎤ i Pi Ai Ai Pi − αPi I Adi Q Pi ⎢ ⎥ j ∗ −eαh Q 0 ⎣ ⎦ < 0, −1 T i U Uik ∗ ∗ − ρ∗ Q ik ⎡ ⎤ −eαh ρ∗ Pj Pj I EjT Pj EjT ⎢ ⎥ ⎢ ⎥ < 0, ∗ −Pi 0 ⎣ ⎦ −1 −αh ∗ ∗ ∗ −e Qi ρ ∀i, j ∈ N ∀i, j ∈ N 3.40 i , ∀i ∈ N λ1 R−1 < Pi < R−1 , λ2 R−1 < Q ⎤ ⎡ 2 −αTf c1 c1 −c2 e ⎥ ⎢ ∗ −λ1 0 ⎥<0 ⎢ ⎣ 1 −αh ⎦ ∗ ∗ − ∗ e λ2 ρ h hold with average dwell time τa > τa∗ Tf αh ln ρ∗ 2 −αT . ln c2 e f − ln 1/λ1 ρ∗ heαh /λ2 c12 System 3.1a–3.1c with wt ≡ 0 is finite-time stable with respect to c12 , c22 , Tf , R, σt. 3.41 14 Mathematical Problems in Engineering 3.2. H∞ Performance Analysis In this subsection, H∞ performance of the following system is investigated: ẋt Aσt xt Adσt xt − h fσt xt B2σt wt, Δx Eσt xt, t tk , t/ tk k 1, 2, 3, . . . zt Cσt xt, xt ϕt, 3.42a 3.42b 3.42c t ∈ t0 − h, t0 3.42d i R−1/2 Qi R−1/2 for all i ∈ Theorem 3.6. R is a positive definite matrix. Let Pi R−1/2 Pi R−1/2 , Q ∗ N. Suppose that there exist positive scalars ρi ≥ 1, i ∈ N, ρ max{ρi , i ∈ N}, α, γ, ε and symmetric positive matrices Pi , Pj , Qi for all i, j ∈ N such that 1 i ≤ 0, j I Ei −T − Q I Ei −1 Q ρ∗ ∀i, j ∈ N ⎤ ⎡ i B2i Pi ATi Ai Pi − αPi I Adi Q Pi Pi CiT ⎥ ⎢ j 0 ⎢ ∗ −eαh Q 0 0 ⎥ ⎥ ⎢ 2 ⎥ ⎢ 0 ∗ ∗ −γ 0 ⎥ < 0, ∀i, j ∈ N ⎢ ⎢ T ∗ −1 ∗ ∗ ∗ − ρ Qi Uik Uik 0 ⎥ ⎦ ⎣ ∗ ∗ ∗ ∗ −I ⎤ ⎡ −eαh ρ∗ Pj Pj I EjT Pj EjT ⎥ ⎢ ⎥ < 0, ∀i, j ∈ N ⎢ ∗ −Pi 0 ⎦ ⎣ −1 ∗ ∗ −e−αh ρ∗ Q i Pi < R−1 , 3.43 3.44 3.45 ∀i ∈ N 3.46 −c22 eαTf γ 2 d2 < 0 3.47 hold with average dwell time τa > τa∗ Tf αh ln ρ∗ h . max 2 αT 2 2 , f ε ln c2 − ln e γ d 3.48 Then, system 3.42a–3.42d is finite-time bounded and has H∞ performance with respect to 0, c22 , Tf , d2 , γ, R, σt, where γ 2 e1εαTf ρ∗ εTf /h γ 2 . Proof. When t ∈ tk , tk1 , σt ik , ik ∈ N, k 0, 1, 2, 3, . . .. Choose the following Lyapunov functional candidate for system 3.42a–3.42d −1 xt V t x tPσt T t t−h −1 xsds. vsxT seαt−s Q σs 3.49 Mathematical Problems in Engineering 15 When t ∈ tk , tk1 , V̇ xt − αV xt zT tzt − γ 2 wT twt ≤ X T tΨk Xt, 3.50 where X T t xT t xT t − h wT t, ⎡ ⎤ Adik Pi−1 B2ik Δk Pi−1 k k ⎢ ⎥ −1 Ψk ⎣ ∗ −eαh Q 0 ⎦, ik−m ∗ ∗ −γ 2 I 3.51 −1 − αP −1 UT Uik P −1 P −1 CT Cik . Δk ATik Pi−1 Pi−1 Aik ρ∗ Q ik ik ik ik ik ik k k Using Schur complement, we obtain from 3.44 that ⎡ ⎤ Ei Pi−1 Adi Pi−1 B2i ⎢ ⎥ −1 0 ⎦ < 0, ⎣ ∗ −eαh Q j ∗ ∗ −γ 2 I 3.52 −1 − αP −1 UT Ui P −1 P −1 CT Ci . where Ei ATi Pi−1 Pi−1 Ai ρ∗ Q i i i i i i Noticing that the above inequality holds for all i, j ∈ N, then we have Ψk < 0, for ik , ik−m ∈ N. Thus, V̇ xt − αV xt zT tzt − γ 2 wT twt < 0, 3.53 Let γ 2 wT sws − zT szs Δs, from 3.32, we have V t < e αt−t0 αh ∗ e ρ Nσ t0 ,t V t0 t Nσ s,t eαt−s eαh ρ∗ Δsds. 3.54 t0 Under zero initial condition, we have t 0< Nσ s,t eαt−s eαh ρ∗ Δsds, 3.55 t0 that is, t t Nσ s,t Nσ s,t eαt−s eαh ρ∗ zT szsds < eαt−s eαh ρ∗ γ 2 wT swsds. t0 3.56 t0 Noticing that t t0 t Nσ s,t eαt−s eαh ρ∗ zT szsds > zT szsds. t0 3.57 16 Mathematical Problems in Engineering Then, we have t Nσ s,t Nσ t0 ,t t eαt−s eαh ρ∗ γ 2 wT swsds < eαt eαh ρ∗ γ 2 wT swsds. t0 3.58 t0 Let t Tf , because τa > h/ε, we have Tf z szsds < e T 1εαTf εT /h ρ∗ f γ 2 t0 Tf 3.59 wT swsds, t0 then Tf z szsds < γ T 2 t0 Tf 3.60 wT swsds. t0 Thus, system 3.42a–3.42d is finite-time bounded and has H∞ performance with respect to 0, c22 , Tf , d2 , γ, R, σt, where γ 2 e1εαTf ρ∗ εTf /h γ 2 . The proof is completed. Remark 3.7. When ρ∗ 1, Theorem 3.6 degenerates to the result of 41, which cannot guarantee the finite-time boundedness of the addressed system if ρ∗ > 1. 3.3. Robust Finite-Time H∞ Control Consider system 2.1a–2.1d, under the switching controller u1 t Kσt xt, t / tk and impulsive controller u2 tk K σt xtk , t tk , the corresponding closed-loop system is given by dσt xt − h fσt xt B2σt wt, σt B1σt Kσt xt A ẋt A Δx Eσt K σt xt, t tk , k 1, 2, 3, . . . zt Cσt Dσt Kσt xt, xt ϕt, t ∈ t0 − h, t0 . t / tk 3.61a 3.61b 3.61c 3.61d i Theorem 3.8. Consider impulsive switched system 2.1a–2.1d, let Pi R−1/2 Pi R−1/2 , Q R−1/2 Qi R−1/2 for all i ∈ N. If there exist positive scalars ρi ≥ 1, i ∈ N, ρ∗ max{ρi , i ∈ N} α, γ, ε, δi and positive definite symmetric matrices Pi , Qi , and matrices Yi , i ∈ N, with appropriate dimensions, such that the following inequalities hold Mathematical Problems in Engineering 17 1 i ≤ 0, j I Ei −T − Q I Ei −1 Q ρ∗ ∀i, j ∈ N ⎤ ⎡ T T i B2i Γi Adi Q Pi EAi Pi Pi CiT YiT DiT YiT EBi ⎥ ⎢ ⎥ ⎢ ⎥ ⎢ ∗ −eαh Q T 0 0 0 Qi EAdi ⎥ ⎢ j ⎥ ⎢ 2 ∗ −γ 0 0 0 ⎥ < 0, ⎢∗ ⎥ ⎢ T ∗ −1 ⎥ ⎢∗ ∗ ∗ − ρ Qi Uik Uik 0 0 ⎥ ⎢ ⎥ ⎢ ⎦ ⎣∗ ∗ ∗ ∗ −I 0 ∗ ∗ ∗ ∗ ∗ −δi 3.62 ∀i, j ∈ N, 3.63 where T Γi Pi ATi YiT B1i Ai Pi B1i Yi − αPi I δi Hi HiT , ⎤ ⎡ αh ∗ −e ρ Pj Pj ⎦ < 0, ∀i, j ∈ N ⎣ ∗ −Pi Pi < R−1 , 3.64 i ∈ N, 3.65 −c22 eαTf γ 2 d2 < 0. 3.66 Then, under the controller Ki Yi Pi−1 , K i −Ei , and the following average dwell time scheme τa > τa∗ Tf αh ln ρ∗ h , max 2 αT 2 2 , f ε ln c2 − ln e γ d 3.67 the corresponding closed-loop system is finite-time bounded with H∞ performance with respect to 0, c22 , Tf , d2 , γ, R, σt and γ 2 e1εαTf ρ∗ εTf /h γ 2 . Proof. According to Assumption 2.1, we have i B1i Ki Ai B1i Ki Hi Fi EAi EBi Ki , A di Adi Hi Fi EAdi . A 3.68 i B1i Ki , A di , Ci Di Ki , we can obtain Now replacing Ai , Adi , Ci in the left side of 3.44 with A that ⎤ ⎡ i B2i Ωi Adi Hi Fi EAdi Q Pi Pi Ci Di Ki T ⎥ ⎢ j ⎥ ⎢∗ −eαh Q 0 0 0 ⎥ ⎢ 2 ⎥, ⎢ 0 0 ∗ −γ Θij ⎢ ∗ ⎥ ⎥ ⎢∗ T ∗ −1 ∗ ∗ − ρ Qi Uik Uik 0 ⎦ ⎣ ∗ ∗ ∗ ∗ −I 3.69 18 Mathematical Problems in Engineering where Ωi Ai B1i Ki Hi Fi EAi EBi Ki Pi Pi Ai B1i Ki Hi Fi EAi EBi Ki T − αPi I. 3.70 From 3.69, we know that Θij Π1ij Π2ij , 3.71 where Π1ij ⎤ ⎡ i B2i Υ1i Adi Q Pi Pi Ci Di Ki T ⎥ ⎢ j 0 ⎥ ⎢ ∗ −eαh Q 0 0 ⎥ ⎢ 2 ⎥, ⎢ 0 0 ∗ ∗ −γ ⎢ ⎥ ⎥ ⎢∗ T ∗ −1 ∗ ∗ − ρ Qi Uik Uik 0 ⎦ ⎣ ∗ ∗ ∗ ∗ −I ⎡ ⎤ i 0 0 0 Υ2i Hi Fi EAdi Q ⎢∗ 0 0 0 0⎥ ⎢ ⎥ ⎢ ⎥ Π2ij ⎢ ∗ ∗ 0 0 0⎥, ⎢ ⎥ ⎣∗ ∗ ∗ 0 0⎦ ∗ ∗ ∗ ∗ 0 3.72 with Υ1i Pi Ai B1i Ki T Ai B1i KPi − αPi I, Υ2i Pi EAi EBi Ki T FiT HiT Hi Fi EAi EBi Ki Pi , 3.73 let Yi Ki Pi , then T Ai Pi B1i Yi − αPi I, Υ1i Pi ATi YiT B1i T T FiT HiT Hi Fi EAi Pi EBi Yi . Υ2i YiT EBi Pi EAi 3.74 Mathematical Problems in Engineering 19 From Lemma 2.11, we can obtain that ⎡ ⎤ Hi ⎢0⎥ ⎢ ⎥ ⎢ ⎥ i 0 0 0 Θij Π1ij ⎢ 0 ⎥Fi EAi Pi EBi Yi EAdi Q ⎢ ⎥ ⎣0⎦ 0 ⎡ ⎤ T T YiT EBi Pi EAi ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ T Qi EAdi ⎢ ⎥ ⎢ ⎥Fi HiT 0 0 0 0 0 ⎢ ⎥ ⎢ ⎥ ⎣ ⎦ 0 0 ⎡ ⎤ Hi ⎢0⎥ ⎢ ⎥ ⎢ ⎥ ≤ Π1ij δi ⎢ 0 ⎥ HiT 0 0 0 0 ⎢ ⎥ ⎣0⎦ 0 ⎡ ⎤ T T YiT EBi Pi EAi ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ T 1⎢ Qi EAdi ⎥ i 0 0 0 . ⎢ ⎥ EAi Pi EBi Yi EAdi Q 0 ⎥ δi ⎢ ⎢ ⎥ ⎣ ⎦ 0 0 3.75 Using Schur complement lemma, we get from 3.63 that Θij < 0. 3.76 Now we choose K i −Ei , and replacing Ei in 3.45 with Ei K i , we know that ⎡ ⎤ 0 −eαh ρ∗ Pj Pj ⎢ ⎥ ∗ −Pi 0 ⎣ ⎦ < 0, −1 ∗ ∗ −e−αh ρ∗ Q i 3.77 by 3.64, we know that the condition3.45 hold. Then, system 2.1a–2.1d is robust finite-time bounded with H∞ performance with respect to 0, c22 , Tf , d2 , γ, R, σt, and γ 2 e1εαTf ρ∗ εTf /h γ 2 . The proof is completed. Remark 3.9. In order to eliminate the impulsive jump, we design an impulsive feedback controller K i −Ei , t tk . Then the system becomes a switched system with continuous states. 20 Mathematical Problems in Engineering 4. Numerical Examples In this section, we present two examples to illustrate the effectiveness of the proposed approach. Example 4.1. Consider system 2.1a–2.1d with the following parameters. Subsystem 1 ! A1 ! ! " −1.3 0.1 −0.1 , H1 0.2 −1 0.2 ! ! " " 0.43 0 0.1 0 E1 , U1 , 0 0.15 0 0.1 ! ! " 0.2 0.1 1 EB1 , B21 0 −0.3 2 ! " ! " 1 1 0.8 0 , D1 , EA1 C1 0 2 0 0.2 " −8 1 , 2 −7 Ad1 " 0.3 , 0.4 B11 EAd1 ! " 3 −3 , 0 4 " −1 , 1 ! " −0.3 −0.1 , 0.2 −0.1 ! " 0.2 0.1 , 0.3 −0.2 4.1 f1 xt 0.1 sin xt, where f1 xt < U1 xt. Subsystem 2 ! ! ! ! " " " " −7 2 −1.2 0.1 −0.1 0.2 −0.3 0.1 , Ad2 , H2 , EAd2 , 1 −6 0.3 −1.1 −0.2 −0.1 0.2 −0.3 ! ! ! ! " " " " 0.15 0 0.2 0 4 −1 −0.3 0.1 E2 , U2 , B12 , EB2 , 0 0.4 0 0.18 1 6 0 0.2 ! ! ! ! " " " " −1 0 2 1 0.8 0 0.1 0.3 B22 , C2 , D2 , EA2 , 2 0.8 0 3 1 −1 0.2 −0.2 4.2 A2 f2 xt 0.18 cos xt, where f2 xt < U2 xt. Choosing Tf 12, h 0.2, d2 10, R I, α 0.1, C22 2, ε 0.1, γ 2 0.5441, ρ∗ 1, solving the LMIs in 3.62–3.66 leads to Mathematical Problems in Engineering 21 ! ! " " 1.3506 −0.1265 0.0234 2 0.5042 0.0525 , , Q Y1 −0.1265 0.7891 0.0525 0.3221 0.1631 ! ! ! " " −0.0001 −0.5221 0.9887 0.0011 0.9995 Y2 , P1 , P2 0.1109 0.0371 0.0011 0.9921 −0.0001 ! " ! " 0.0241 −0.3605 −0.0001 −0.5218 , K2 , K1 0.1647 0.2699 0.1109 0.0371 1 Q ! −1 Q 1 − I E1 T −1 I Q 1 " −0.3577 , 0.2680 " −0.0001 , 1.0006 4.3 E1 ≤ 0, −1 − I E2 T Q −1 I E2 ≤ 0, Q 2 1 −1 − I E2 T Q −1 I E2 ≤ 0, Q 2 2 −1 − I E1 T Q −1 I E1 ≤ 0, Q 2 1 τa > τa∗ 1.2049, we choose τa 2, γ 2 e1εαTf ρ∗ εαTf γ 2 2.0368, then the system is finite-time bounded according to 41, Theorem 3. Example 4.2. Consider system 2.1a–2.1d with the following parameters. Subsystem 1 ! ! ! ! " " " " −8 1 −1.3 0.1 −0.1 0.3 0.2 0.1 , Ad1 , H1 , EAd1 , 2 −7 0.2 −1 0.2 0.4 0.3 −0.2 ! ! ! ! " " " " −0.1 0 0.01 0 3 −3 0.2 0.1 E1 , U1 , B11 , EB1 , 0 −0.1 0 0.01 0 4 0 −0.3 ! ! ! ! " " " " 1 −1 −3 1 8 0 −3 −0.1 B21 , C1 , D1 , EA1 , 2 1 0 −2 0 2 0.2 −1 A1 4.4 f1 xt 0.01 sin xt. Subsystem 2 ! " ! " ! " ! " −7 2 −1.2 0.1 −0.1 0.2 −0.3 0.1 , Ad2 , H2 , EAd2 , 1 −6 0.3 −1.1 −0.2 −0.1 0.2 −0.3 ! " ! " ! " ! " −0.1 0 0.02 0 4 −1 −0.3 0.1 E2 , U2 , B12 , EB2 , 0 −0.1 0 0.08 1 6 0 0.2 ! ! ! ! " " " " −1 0 −2 1 8 0 −1 0.3 B22 , C2 , D2 , EA2 , 2 0.8 0 −3 1 8 0.2 −2 4.5 A2 f2 xt 0.02 cos xt. 22 Mathematical Problems in Engineering 1 Let h 0.2, Tf 12, d2 10, R I, α 0.001, C22 21, ρ∗ 1.3, γ 2 0.9344. By solving the LMIs in 3.62–3.66, we can get ! 0.4252 Q1 0.0387 ! 0.1064 Y2 −0.1260 " 0.0387 , 1.2272 " −0.2575 , 0.2934 ! 0.2329 K1 −0.2389 ! ! " " 0.4352 0.0470 0.0866 −0.4834 Q2 , Y1 , 0.0470 1.2369 −0.0863 0.5554 ! ! " " 0.4606 0.0418 0.5364 −0.0611 P1 , P2 , 0.0418 0.9965 −0.0611 0.9884 " ! " −0.4949 0.1699 −0.2500 , K2 , 0.5673 −0.2024 0.2844 4.6 and τa > τa∗ 3.8340. We choose τa 4, ε 0.05, γ 2 0.9464, the initial condition xt 0, t ∈ −h, 0, the switching signal is shown in Figure 1, and state trajectories of the closed-loop system are shown in Figure 2. We can see from Figure 2 that the states of the system are continuous due to the feedback K i in impulsive instants. 2 Let h 0.2, Tf 12, d2 10, R I, and α 0.001. By solving the LMIs of 41, Theorem 3, we can get ! " 0.4015 0.0359 , Q1 0.0359 1.0563 ! " 0.1279 −0.2380 Y2 , −0.1006 0.2699 ! 0.2349 K1 −0.1896 ! " ! " 0.5224 0.1104 0.1245 −0.6523 Q2 , Y1 , 0.1104 1.0717 −0.0998 0.5952 ! " ! " 0.5577 0.0099 0.5577 0.0099 P1 , P2 , 0.0099 0.9992 0.0099 0.9992 ! " " −0.6552 0.2336 −0.2405 , K2 , 0.5976 −0.1852 0.2720 4.7 −1 I E1 > 0, −1 − I E1 T Q Q 1 1 −1 − I E2 T Q −1 I E2 > 0, Q 2 1 −1 − I E2 T Q −1 I E2 > 0, Q 2 2 −1 − I E1 T Q −1 I E1 > 0. Q 2 1 Obviously, the above inequalities do not satisfy the conditions of 41, Theorem 3. Thus, we cannot draw the conclusion that the closed-loop system is finite-time bounded from Theorem 3 in 41. 5. Conclusions This paper has investigated robust finite-time H∞ control for a class of impulsive switched nonlinear systems with time-delay. Based on piecewise Lyapunov function, sufficient conditions which guarantee finite-time boundedness of the impulsive switched system are Mathematical Problems in Engineering 23 2.5 System modes 2 1.5 1 0.5 0 2 4 6 8 10 12 10 12 t (s) Figure 1: Switching signal. 0.3 0.2 0.1 0 x −0.1 −0.2 −0.3 −0.4 0 2 4 6 8 t (s) x1 x2 Figure 2: State trajectories of the closed-loop system. derived. Then, a feedback control scheme consisting of an impulsive feedback controller and a switching controller is proposed, and the proposed control strategy can guarantee that the closed-loop system is finite-time bounded with H∞ disturbance attenuation level. Finally, the results are illustrated by means of two numerical examples. 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