Sn+→ the set of n×n symmetric positive definite matrices |
Rm→ m-dimensional Euclidean space |
A⊤→ The transpose of the A matrix |
Sym(P)→ P+P⊤, For any square matrix P |
0→ A zero matrix with appropriate dimensions |
Citation: Junkang Tian, Zerong Ren, Shouming Zhong. Stability analysis for time delay systems via a generalized double integral inequality[J]. AIMS Mathematics, 2020, 5(6): 6448-6456. doi: 10.3934/math.2020415
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A time delay widely exists in many fields such as chemistry, biology, industry, and so on. Since a time delay arising in a system may cause instability, the stability analysis of time-delay systems has been wildly studied in the past few decades [1,2]. The main purpose is paid to determine the admissible delay, for which the systems remain stable.
It is well known that the LKF method has been widely used to obtain stability conditions for time-delay systems [3,4]. The main purpose of the LKF method is to estimate the integral term arising in the time derivative of double integral term in the LKF. Therefore, to get less conservative stability criteria, many integral inequality methods are derived. Those inequality methods include Jensen inequality [5,6], Wirtinger inequality [7,8,9], double integral inequlity [10,11,12], various improved integral inequalities [13,14,15,16,17,18,19,20,21,22,23,24,25,26]. The Jensen inequality expressed as Vab(˙y)=∫ba˙yT(t)R˙y(t)dt≥1b−aΩT0RΩ0=VJensen, where a<b,R=RT>0,Ω0=y(b)−y(a). The Wirtinger-based inequality expressed as Vab(˙y)≥VJensen+3b−aΩT1RΩ1=VSeuret, where Ω1=y(b)+y(a)−2b−a∫bay(t)dt. The further improved inequality expressed asVab(˙y)≥VSeuret+5b−aΩT2RΩ2, Vab(˙y)≥VSeuret+5b−aΩT2RΩ2+7b−aΩT3RΩ3, Vab(˙y)≥VSeuret+5b−aΩT2RΩ2+7b−aΩT3RΩ3+9b−aΩT4RΩ4 in [13,14,15], respectively, where Ω2,Ω3,Ω4 are defined in Lemma 4 [15]. However, these results only estimate the integral term arising in the time derivative of double integral term in the LKF. This paper presents a generalized double integral inequality which includes those in [10,11,12] as special cases. A new stability criterion is proposed by choosing a new LKF and using the generalized double integral inequality. Both the generalized integral inequality and the new LKF include fourth integrals, which may yield less conservative results. Two examples are introduced to show the effectiveness of the proposed criterion. The contributions of our paper are as follows:
∙ The integral −∫ba∫bu˙xT(s)P˙x(s)dsdu is estimated as−∫ba∫bu˙xT(s)P˙x(s)dsdu≤ζTωζ, where ω and ζ are defined in Lemma 3. The above inequality includes those in [10,11,12] as special cases.
∙ Both the new double integral inequality and the new LKF include fourth integrals, which may obtain more general results.
Notation: See Table 1.
Sn+→ the set of n×n symmetric positive definite matrices |
Rm→ m-dimensional Euclidean space |
A⊤→ The transpose of the A matrix |
Sym(P)→ P+P⊤, For any square matrix P |
0→ A zero matrix with appropriate dimensions |
Consider the time delay systems as
˙y(t)=Ay(t)+By(t−h)+C∫tt−hy(s)ds | (2.1) |
y(t)=ϕ(t),t∈[−h,0] | (2.2) |
where y(t)∈Rn is the state vector, h>0 is constant time-delay and the initial condition ϕ(t) is a continuous function.
Lemma 1. [15] For a matrix P∈Sn+, and any continuously differentiable function x:[a,b]⟶Rn, then we can obtain
∫ba˙xT(s)P˙x(s)ds≥1b−a4∑i=0(2i+1)ΩTiPΩi | (2.3) |
where
Ω0=x(b)−x(a) |
Ω1=x(b)+x(a)−2b−a∫bax(t)dt |
Ω2=x(b)−x(a)+6b−a∫bax(t)dt−12(b−a)2∫ba∫bux(t)dtdu |
Ω3=x(b)+x(a)−12b−a∫bax(t)dt+60(b−a)2∫ba∫bux(t)dtdu−120(b−a)3∫ba∫bu∫bvx(t)dtdvdu |
Ω4=x(b)−x(a)+20b−a∫bax(t)dt−180(b−a)2∫ba∫bux(t)dtdu+840(b−a)3∫ba∫bu∫bvx(t)dtdvdu−1680(b−a)4∫ba∫bu∫bv∫bβx(t)dtdβdvdu |
Lemma 2. [27] For a positive define matrix P∈Sn+, a integrable function {x(s)|s∈[a,b]}, and any auxiliary functions {fi(s)|i∈[0,n],s∈[a,b],f0(s)=1} satisfying ∫ba∫bufi(s)fj(s)dsdu=0, (0≤i,j≤n,i≠j) with fi(s)≠0,i=1,2,⋯,n. Let λi∈Rn×k,i=0,1,⋯,n and a vector ζ∈Rk, such that∫ba∫bufi(s)x(s)dsdu=λiζ. Then for any matrices Mi∈Rk×n(i=0,1,⋯,n), the following inequality holds
−∫ba∫buxT(s)Px(s)dsdu≤ζT{n∑i=0∫ba∫buf2i(s)dsduMiP−1MTi+Sym(n∑i=0Miλi)}ζ | (2.4) |
Proof. Define M=[MT0MT1⋯MTn]T, ξ(s)=[f0(s)ζTf1(s)ζT⋯fn(s)ζT]T.
It is easy to obtain that
−2ξT(s)Mx(s)≤ξT(s)MP−1Mξ(s)+xT(s)Px(s) | (2.5) |
Integrating the inequality (2.5) from [a,b]×[u,b] yields
−2ζTn∑i=0Mi∫ba∫bufi(s)x(s)dsdu≤ζT{n∑i=0∫ba∫buf2i(s)dsduMiP−1MTi+2n∑i=0n∑j=i+1∫ba∫bufi(s)fj(s)dsduMiP−1MTi}ζ+∫ba∫buxT(s)Px(s)dsdu=ζT{n∑i=0∫ba∫buf2i(s)dsduMiP−1MTi}ζ+∫ba∫buxT(s)Px(s)dsdu | (2.6) |
This completes the proof.
Lemma 3. For a differential function x:[a,b]→Rn, a matrix P∈Rn+, a vector ζ∈Rk, and any matrices Mi∈Rk×n(i=1,2,3,4), then the following inequality holds:
−∫ba∫bu˙xT(s)P˙x(s)dsdu≤ζTωζ | (2.7) |
where
ω=(b−a)22(M1P−1MT1+12M2P−1MT2+13M3P−1MT3+14M4P−1MT4)+(b−a)Sym(M1λ1+M2λ2+M3λ3+M4λ4) |
λ1ζ=x(b)−1b−a∫bax(s)ds |
λ2ζ=x(b)+2b−a∫bax(s)ds−6(b−a)2∫ba∫bux(s)dsddu |
λ3ζ=x(b)−3b−a∫bax(s)ds+24(b−a)2∫ba∫bux(s)dsdu−60(b−a)3∫ba∫bu∫bvx(s)dsdvdu |
λ4ζ=x(b)+4b−a∫bax(s)ds−60(b−a)2∫ba∫bux(s)dsdu+360(b−a)3∫ba∫bu∫bvx(s)dsdvdu−840(b−a)4∫ba∫bu∫bv∫bβx(s)dsdβdvdu |
Proof. The result can be easily obtained by choosing n=3, f1(s)=3b−a(s−2b+a3), f2(s)=10(b−a)2[(s−3b+2a5)2−3(b−a)250], f3(s)=−4+30s−ab−a−60(s−ab−a)2+35(s−ab−a)3in (2.4). So the details of proof is omitted.
Remark 1. The inequality (25) of Lemma 5.1 in [10] is a special case of Lemma 3 by setting M1=−2b−aλT1R, M2=−4b−aλT2R, M3=0, and M4=0. The inequality (4) of Lemma 2.3 in [11] is a special case of Lemma 3 by setting M1=−2b−aλT1R, M2=−4b−aλT2R, M3=−6b−aλT3R, and M4=0. In addition, the inequality (12) of Lemma 5 in [12] is a special case of Lemma 3 by set ting M1=−2b−aλT1R, M2=−4b−aλT2R, M3=−6b−aλT3R, and M4=−8b−aλT4R.
Based on Lemma 1 and Lemma 3, a new stability condition can be obtained.
Theorem 1. System (1) is asymptotically stable if there exist matrices P∈S5n+, R1,R2,R3∈Sn+, and any matrices M1,M2,M3,M4∈R6n×n such that
Ψ=Sym(ΠT1PΠ2)+δT1R1δ1−δT2R1δ2+h2δT0R2δ0+h22δT0R3δ0−ΠT3R2Π3−3ΠT4R2Π4−5ΠT5R2Π5−7ΠT6R2Π6−9ΠT7R2Π7+h22(M1R−13MT1+12M2R−13MT2+13M3R−13MT3+14M4R−14MT4)+hSym(M1Π8+M2Π9+M3Π10+M4Π11)<0 | (3.1) |
where
Π1=[δT1δT3δT4δT5δT6]T,
Π2=[δT0δT1−δT2hδT1−δT3h22δT1−δT4h36δT1−δT5],
Π3=δ1−δ2,
Π4=δ1+δ2−2hδ3,
Π5=δ1−δ2+6hδ3−12h2δ4,
Π6=δ1+δ2−12hδ3+60h2δ4−120h3δ5,
Π7=δ1−δ2+20hδ3−180h2δ4+840h3δ5−1680h4δ6,
Π8=δ1−1hδ3,
Π9=δ1+2hδ3−6h2δ4,
Π10=δ1−3hδ3+24h2δ4−60h3δ5,
Π11=δ1+4hδ3−60h2δ4+360h3δ5−840h4δ6,
δ0=Aδ1+Bδ2+Cδ3,
δi=[0n×(i−1)nIn0n×(7−i)n], i=1,2,⋯,6.
Proof. Introduce a LKF as
V(yt)=ζT(t)Pζ(t)+∫tt−hyT(s)R1y(s)ds+h∫tt−h∫tu˙yT(s)R2˙y(s)dsdu+∫tt−h∫tu∫tv˙yT(s)R3˙y(s)dsdvdu | (3.2) |
where
ζ(t)=[yT(t)∫tt−hyT(s)dsvT1(t)vT2(t)vT3(t)]T
vT1(t)=∫tt−h∫tu1yT(s)dsdu1
vT2(t)=∫tt−h∫tu1∫tu2yT(s)dsdu2du1
vT3(t)=∫tt−h∫tu1∫tu2∫tu3yT(s)dsdu3du2du1
Then, the time derivative of V(yt) along the trajectories of system (1) as follows
˙V(yt)=2ζT(t)P˙ζ(t)+yT(t)R1y(t)−yT(t−h)R1y(t−h)+h2˙yT(t)R2˙y(t)+h22˙yT(t)R3˙y(t)−h∫tt−h˙yT(s)R2˙y(s)ds−∫tt−h∫tu˙yT(s)R3˙y(s)dsdu=ηT(t){Sym(ΠT1PΠ2)+δT0Qδ0−δT7Qδ7+δT1R1δ1−δT2R1δ2+h2δT0R2δ0+h22δT0R3δ0}η(t)−h∫tt−h˙yT(s)R2˙y(s)ds−∫tt−h∫tu˙yT(s)R3˙y(s)dsdu | (3.3) |
where
η(t)=[yT(t)yT(t−h)∫tt−hyT(s)dsvT1(t)vT2(t)vT3(t)]T
By Lemma 1, we have
−h∫tt−h˙yT(s)R2˙y(s)ds≤ηT(t)(−ΠT3R2Π3−3ΠT4R2Π4−5ΠT5R2Π5−7ΠT6R2Π6−9ΠT7R2Π7)η(t) | (3.4) |
By Lemma 3, we have
−∫tt−h∫tu˙yT(s)R3˙y(s)dsdu≤ηT(t)[h224∑i=11iMiR−13MTi+hSym(4∑i=1MiΠi+7)]η(t) | (3.5) |
Thus, according to (3.2)–(3.5), we have ˙V(yt)≤ηT(t)Ψη(t). Thus, if (3.1)holds, then, for a sufficient small scalar ε>0, ˙V(yt)≤−ε‖y(t)‖2 holds, which ensures system (1) is asymptotically stable. The proof is completed.
Remark 2. Both the double integral inequality and the new LKF include fourth integrals, which may yield novel stability results. Furthermore, in order to fully consider relevant information of the double integral inequality in Lemma 3, the ∫tt−h∫tu1∫tu2∫tu3yT(s)dsdu3du2du1 is added as a state vector.
In this section, we demonstrate the advantages of our proposed criterion by two numerical examples.
Example 1. Consider system(1) with:
A=[0.200.20.1], B=[0000], C=[−10−1−1].
Table 2 lists the allowable upper bounds of h by different methods. Table 2 shows that the maximum delay bounds of h obtained by our method are much larger than those in [4,6,7,9,11].
methods | Maximal h | NoDv |
[7] | 1.877 | 16 |
[9] | 1.9504 | 59 |
[4] | 2.0395 | 75 |
[6] | 2.0395 | 27 |
[11] | 2.0402 | 45 |
Theorem 1 | 2.0412 | 64 |
Example 2. Consider system(1) with:
A=[01−100−1], B=[0.00.10.10.2], C=[0000]
Table 3 lists the allowable upper bounds of h by different methods. Table 3 shows that the maximum delay bounds of h obtained by our method are much larger than those in [4,7,9,10,11,14]. For h=0.750, y(0)=(0.001,−0.001)T, the state trajectories of the system(1) is given in Figure 1.
methods | Maximal h | NoDv |
[7] | 0.126 | 16 |
[9] | 0.126 | 59 |
[4] | 0.577 | 75 |
[10] | 0.577 | 96 |
[11] | 0.675 | 45 |
[14] | 0.728 | 45 |
Theorem 1 | 0.750 | 64 |
Remark 3. According to Example 1 and Example 2, although our method can reduce the conservatism of the system effectively, it increases the computational burden.
This paper focus on a new stability condition for a class of time delay systems. By using two generalized integral inequalities and a new augmented LKF, a new stability criterion is obtained. Both the double integral inequality and the new LKF include fourth integrals, which may yield more general results. Two numerical examples are proposed to show the effectiveness of the proposed criterion.
This work was supported by New Academic Talents and Innovation Exploration Project of Department of Science and Technology of Guizhou Province of China under Grant (Qian ke he pingtai rencai [2017] 5727-19); Innovative Groups of Education Department of Guizhou Province (Qian jiao he KY [2016] 046).
The authors declare that there are no conflicts of interest.
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1. | Xiang Liu, Dianli Zhao, New stability criterion for time-delay systems via an augmented Lyapunov–Krasovskii functional, 2021, 116, 08939659, 107071, 10.1016/j.aml.2021.107071 | |
2. | Jun Hui Lee, Jung Hoon Kim, PooGyeon Park, A generalized multiple-integral inequality based on free matrices: Application to stability analysis of time-varying delay systems, 2022, 430, 00963003, 127288, 10.1016/j.amc.2022.127288 | |
3. | Dongmei Xia, Kaiyuan Chen, Lin Sun, Guojin Qin, Research on reachable set boundary of neutral system with various types of disturbances, 2025, 20, 1932-6203, e0317398, 10.1371/journal.pone.0317398 |
Sn+→ the set of n×n symmetric positive definite matrices |
Rm→ m-dimensional Euclidean space |
A⊤→ The transpose of the A matrix |
Sym(P)→ P+P⊤, For any square matrix P |
0→ A zero matrix with appropriate dimensions |
Sn+→ the set of n×n symmetric positive definite matrices |
Rm→ m-dimensional Euclidean space |
A⊤→ The transpose of the A matrix |
Sym(P)→ P+P⊤, For any square matrix P |
0→ A zero matrix with appropriate dimensions |
methods | Maximal h | NoDv |
[7] | 1.877 | 16 |
[9] | 1.9504 | 59 |
[4] | 2.0395 | 75 |
[6] | 2.0395 | 27 |
[11] | 2.0402 | 45 |
Theorem 1 | 2.0412 | 64 |
methods | Maximal h | NoDv |
[7] | 0.126 | 16 |
[9] | 0.126 | 59 |
[4] | 0.577 | 75 |
[10] | 0.577 | 96 |
[11] | 0.675 | 45 |
[14] | 0.728 | 45 |
Theorem 1 | 0.750 | 64 |