Journal of Control Theory and Applications 2007 5 (4) 409–414 DOI 10.1007/s11768-006-6030-2
Delay-dependent robust stabilization for a class of
neutral systems with nonlinear perturbations
Ming LI
1
, Guangda HU
2
(1. Center of Control Theory and Guidance Technology, Harbin Institute of Technology, Harbin Heilongjiang 150001, China;
2.School of Information Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China )
Abstract: This note deals with the problem of stabilization/stability for neutral systems with nonlinear perturba-
tions. A new stabilization/stability scheme is presented. Using improved Lyapunov functionals, less conservative stabiliza-
tion/stability conditions are derived for such systems based on linear matrix inequalities (LMI). Numerical examples are
provided to show that the proposed results significantly improve the allowed upper bounds of the delay size over some
existing ones in the literature.
Keywords: Delay-dependent criterion; Robust stabilization/stability; Linear matrix inequality (LMI); Neutral delay
systems; State feedback stabilization; Nonlinear perturbations
1 Introduction
Stability criteria for neutral systems can be classified
into two types: delay-dependent, which include information
on the size of delays, and delay-independent, which are ap-
plicable to delays of arbitrary size. Delay-independent sta-
bility criteria tend to be conservative, especially for small
delays, while delay-dependent ones are usually less con-
servative. A great number of delay-dependent stability re-
sults have been reported in the literature; see e.g., [2∼4,
6∼10, 12∼15, 17∼19], and the references therein. Also, the
problem is extended to neutral systems with perturbations
in [16]. However, the stabilization criteria for such systems
have not been fully investigated.
In this note, we propose a new delay-dependent sta-
bilization/stability scheme for neutral systems with non-
linear perturbations. To obtain less conservative stabiliza-
tion and stability criteria, we propose improved, augmented
Lyapunov functionals that employ free weighting matri-
ces based on [10]. Based on the second Lyapunov method,
delay-dependent stabilization/stability criteria are derived in
terms of linear matrix inequalities (LMI) [1]. Numerical ex-
amples are given to show the superiority of the present re-
sults to those in the other literature.
Notations R
n
is the n-dimensional Euclidean space.
R
m×n
denotes the set of m × n real matrices. ∗ denotes the
symmetric part. X > 0(X > 0) means that X is a real sym-
metric positive-definite matrix (positive-semidefinite). I de-
notes the identity matrix with appropriate dimensions. | · |
refers to the induced matrix 2-norm. diag{· · · } denotes the
block diagonal matrix. C
n,h
= C([−h, 0], R
n
) denotes the
Banach space of continuous functions mapping the interval
[−h, 0] into R
n
, with the topology of uniform convergence.
2 Problem statement
Consider the following system:
˙x(t) = Ax(t) + A
1
x(t − h) + A
2
˙x(t − h)
+ f
1
(t, x(t)) + f
2
(t, x(t − h)) + Bu(t),
x(t) = φ(t), t ∈ [−h, 0], (1)
where x(t) ∈ R
n
is the state vector, u(t) ∈ R
m
is the con-
trol input, A, A
1
, A
2
∈ R
n×n
and B ∈ R
n×m
are known
real parameter matrices, |A
2
| < 1 holds. h > 0 is a constant
positive delay, φ(s) ∈ C
n,h
is a given continuous vector val-
ued initial function, and f
i
(·) is the nonlinear perturbations
in the system. It is assumed that the nonlinear perturbations
are bounded in magnitude as
|f
1
(t, x(t))| 6 α
1
|x(t)|,
|f
2
(t, x(t − h))| 6 α
2
|x(t − h)|, ∀t > 0.
For (1), we will design a state-feedback controller
u(t) = Kx(t), (2)
where K ∈ R
m×n
is a constant matrix.
We need the following lemmas:
Lemma 1 [16] For any vectors a, b ∈ R
n
2 and scalar
ε > 0, 2a
T
b 6 εa
T
a + ε
−1
b
T
b.
Lemma 2 [8] For any constant symmetric matrix Q ∈
R
m×m
, Q = Q
T
> 0, scalar γ > 0, vector function
Received 22 February 2006; revised 8 March 2007.
This work was supported by the National Natural Science Foundation of China (No.10571036).