Improved Exponential Stability Criteria for Uncertain Neutral System with Nonlinear Parameter Pe

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International Journal of Automation and Computing 7(4),November 2010,413—418 

DOI:10.1007/s11633—010—0522—8 

Improved Exponential Stability Criteria for Uncertain 

Neutral System with Nonlinear Parameter Perturbations 

Fang Qiu Bao—Tong Cui 

Department of Mathematics and Information Science,Binzhou University,Binzhou 256603,PRC 。College of Communications and Control Engineering,Jiangnan University,Wuxi 214122,PRC 

Abstract:This paper investigates the problem of robust exponential stability for neutral systems with time—varying delays and 

nonlinear perturbations.Based on a novel Lyapunov functional approach and linear matrix inequality technique,a new delay—dependent 

stability condition is derived.Since the model transformation and bounding techniques for cross terms are avoided,the criteria proposed in this paper are less conservative than some previous approaches by using the free—weighting matrices.One numerical example is 

presented to illustrate the effectiveness of the proposed results. 

Keywords:Neutral system,time—varying delay,exponential stability,nonlinear perturbation,linear matrix inequality(LMI) 

1 Introduction 

Neutra1 time—delay systems are often encountered in 

many practical situations,such as distributed networks, 

population ecology,and processes including steam or heat exchanges[ .The stability of time—delay systems is an 

important problem of recurring interest over the decades. 

since the existence of time delay in systems can cause the systems to be unstable[ . Existing results on this topic 

can be roughly classified into two categories,namely delay— independent criteria[。, and delay—dependent criteria[5—2 . and it is generally recognized that the latter cases are less 

conservative. 

In recent years,the problem of robust stability of neu— 

tral systems with nonlinear Derturbations has also received considerable attention[ , 0—0圳.since nonlinearities may 

cause instability and poor performance of practical sys— 

tems.Various techniques have been proposed by many re— 

searchers to derive the delay—dependent stability criteria for 

these classes of systems,for example,model transformation techniques[ 。 .the improved bounding techniques[ , . and matrix decomposition approaches[ 0, .However.the 

method by model transformation may introduce additiona1 

dynamics or require some additiona1 assumptions.which 

lead to relatively conservative results.One way to further 

improve the results is in virtue of the idec of introducing 

free—weighting matrices.Free—weighting matrices which ex— 

press the relationshiDs between the terms in the Leibniz— 

Newton formula,have been used in many recent papers to 

deal with time-delay systemst 一 .The results can also be 

extended to tile neutral systems with nonlinear perturba— 

tions. 

In addition,the study on neutral systems is mainly fo— 

cused on the discussion of asymptotic stability,and very few 

results exist on the exponentia1 stability criteria for uncer— 

Manuscript received October 10,2009;revised March 1,2010 This work was supported by Natural Science Foundation of Jiangsu Province of China(No.BK2007016)and Scientific Research and De— velopment Program of the Higher Education Institutions of Shan— dong Province of China(No J09LG58). tain neutral systems,especially for the case with nonlinear 

perturbation.However.it is also important to find esti— 

mates of the transient decay rate of a delay system in prac— 

tical applications,which has attracted many researchers to 

study the exponential stability of time—delay systems in re— cent years[ — 驯It should be noted that researches of ex— ponential stability in l 14一l7I have mainly been focused on 

cases with constant delays. But in practice,time delay 

is usually time—varying,which can even largely change the 

dynamics of the system in some cases.Therefore,more 

attention should be paid to exponential stability with time— varying delays. Recently.Chen et a1.【 studied the ro- 

bustly exponential stability problem for neutral systems 

with nonlinear Derturbations.However.the criteria pro— 

posed in[18]are based on the integral inequality technique, 

which can lead to relatively conservative results. 

In this paper,we investigate the problem of expo— 

nential stability of uncertain neutral systems with time— 

varying delay and nonlinear parameter perturbations.A 

new Lyapunov—Krasovskii functional combined with free— 

weighting matrices is introduced to prove the exponential 

stability,and slack matrix variables are used to reduce con— 

servatism.The proposed criterion is expressed in linear 

matrix inequality(LMIs),which can be easily checked by 

utilizing the LMI rr0olbox in Matlab.Meanwhile.tile con—