
results are only applicable to linear 2-D systems. As it is well known, most practical 2-D systems are nonlinear and hence the
results do not work in this case [33]. More recently, based on the T–S fuzzy modeling approach, non-quadratic stabilization
conditions for a class of Roesser-type nonlinear 2-D systems have been proposed in [33], where the non-quadratic control
scheme [16] and the right-hand-side slack variable approach [18,31] are extended to the 2-D T–S fuzzy setting. To further
reduce the conservatism, relaxed stabilization conditions for discrete-time 2-D T–S fuzzy systems have been developed
via improved homogeneous polynomial techniques in [34]. In the existing results [33,34], the so-called right-hand-side slack
variable technique plays an important role in reducing the conservatism. However, the introduction of slack variables leads
to a high computational cost as a trade-off. Now, it seems that the challenge is to improve the quality and efficiency of relax-
ations, i.e., to obtain the same results with lower computational complexity, or to extend a given stability condition to con-
trol synthesis. As stated in [33,34], the conservatism can be further reduced if we change ‘‘something’’, such as the control
law, the form of Lyapunov functions, or exploit the algebraic property of membership functions. This motivates us to carry
out the present work.
This paper considers the stabilization problem of a class of discrete-time 2-D T–S fuzzy systems. Based on a novel non-
PDC scheme and a new homogeneous polynomially parameter-dependent (HPPD) Lyapunov function, new relaxed stabiliza-
tion conditions are proposed. As the degree of HPPD Lyapunov function increases, the conservatism of the obtained stabil-
ization conditions is gradually reduced due to the introduction of extra degrees of freedom. Moreover, by exploiting the
algebraic property of membership functions, the stabilization conditions approach to exactness in the sense of convergence.
In other words, the stabilization conditions are asymptotically necessary and sufficient. Compared with the existing methods
[33,34], no slack variables are introduced in control synthesis, and hence the same or less conservative results can be ob-
tained with a lower computational cost. The effectiveness of the proposed method is illustrated by a numerical example.
The rest of the paper is organized as follows. Problem statement and preliminaries are given in Section 2. New relaxed
non-quadratic stabilization conditions are presented in Section 3. In Section 4, an example is given to illustrate the effective-
ness of the proposed method. Finally, some conclusions are drawn in Section 5.
The notations used in the paper are fairly standard. For example, X > 0 (or X P 0) means the matrix X is symmetric and
positive definite (or symmetric and positive semidefinite). For a square matrix E, He(E) is defined as E + E
T
. X
T
denotes the
transpose of X. The symbol I represents the identity matrix with appropriate dimension. A star ⁄ in a symmetric matrix de-
notes the transposed element in the symmetric position. For a matrix P, min(P) (respectively, max(P)) means the smallest
(respectively, largest) eigenvalue of P. Z
þ
denotes the set of negative integers {0,1,2,...} and M! represents factorial. C
1
de-
notes the space of continuously differentiable functions.
2. Problem formulation and preliminaries
2.1. Discrete-time 2-D T–S fuzzy model
Consider a Roesser-type discrete-time nonlinear 2-D system described by
x
þ
ðs; lÞ¼Zðxðs; lÞÞþSðxðs; lÞÞuðs; lÞ; ð1Þ
x
h
ð0; lÞ¼f ðlÞ; x
v
ðs; 0Þ¼gðsÞ ð2Þ
with
xðs; lÞ¼
x
h
ðs; lÞ
x
v
ðs; lÞ
"#
; x
þ
ðs; lÞ¼
x
h
ðs þ 1; lÞ
x
v
ðs; l þ 1Þ
"#
;
where x
h
ðÞ 2 R
n
1
is the horizonal state, x
v
ðÞ 2 R
n
2
is the vertical state, u() 2 R
m
is the control input. ZðÞ and SðÞ are general
nonlinear functions satisfying Z; S2C
1
. s, l are two integers in Z
þ
. f(l) and g(s) are the corresponding boundary conditions
along two independent directions.
By extending the 1-D T–S fuzzy modeling method [29] to the 2-D case, we can obtain a discrete-time 2-D T–S fuzzy model
described by the following rules
IF z
1
ðs; lÞ is M
i1
; and ...; and z
L
ðs; lÞ is M
iL
; Then;
x
þ
ðs; lÞ¼A
i
xðs; lÞþB
i
uðs; lÞ; i ¼ 1; ...; r;
x
h
ð0; lÞ¼f ðlÞ; x
v
ðs; 0Þ¼gðsÞ
ð3Þ
with
A
i
¼
A
11
i
A
12
i
A
21
i
A
22
i
"#
; B
i
¼
B
1
i
B
2
i
"#
;
where z
p
(s,l), for p =1,...,L are the premise variables, M
ip
is the fuzzy set, r is the number of IF-THEN rules. A
11
i
2 R
n
1
n
1
;
A
12
i
2 R
n
1
n
2
; A
21
i
2 R
n
2
n
1
; A
22
i
2 R
n
2
n
2
; B
1
i
2 R
n
1
m
; B
2
i
2 R
n
2
m
, respectively.
144 D.-W. Ding et al. / Information Sciences 189 (2012) 143–154