Y. Zhu and F. Yang / Simultaneous H
2
/H
∞
Stabilization for Chemical Reaction Systems Based on ··· 3
B
s
2
, C
s
0
, D
s
01
, D
s
02
, C
s
1
, D
s
11
, D
s
12
, C
s
2
, D
s
20
and D
s
21
are the
constant matrices of the s-th subsystem.
We consider the dynamic output feedback controller for
the systems (2) as
˙
ˆx = K
A
ˆx + K
B
y
u = K
C
ˆx
(3)
where ˆx ∈ R
n
c
is the state of the controller, K
A
, K
B
and
K
C
are the controller matrices with compatible dimensions
to be determined.
The controller (3) is applied to the subsystems (2), we
get the closed-loop systems as
⎧
⎪
⎨
⎪
⎩
˙x
s
cl
= A
s
cl
x
s
cl
+ B
s
cl0
ω
s
0
+ B
s
cl1
ω
s
1
z
s
0
= C
s
cl0
x
cl
s
+ D
s
cl0
ω
s
0
z
s
1
= C
s
cl1
x
cl
s
+ D
s
cl1
ω
s
1
(4)
where
x
s
cl
=
(x
s
)
T
(ˆx)
T
T
A
s
cl
=
¯
A
s
+
¯
B
s
K
¯
C
s
=
A
s
B
s
2
K
C
K
B
C
s
2
K
A
B
s
cl0
=
¯
B
s
0
+
¯
B
s
K
¯
D
s
20
=
B
s
0
K
B
D
s
20
B
s
cl1
=
¯
B
s
1
+
¯
B
s
K
¯
D
s
21
=
B
s
1
K
B
D
s
21
C
s
cl0
=
¯
C
s
0
+
¯
D
s
02
K
¯
C
s
=
C
s
0
D
s
02
K
C
C
s
cl1
=
¯
C
s
1
+
¯
D
s
12
K
¯
C
s
=
C
s
1
D
s
12
K
C
D
s
cl0
= D
s
01
+
¯
D
s
02
K
¯
D
s
20
= D
s
01
D
s
cl1
= D
s
11
+
¯
D
s
12
K
¯
D
s
21
= D
s
11
and
K =
K
A
K
B
K
C
0
,
¯
A
s
=
A
s
0
00
,
¯
B
s
0
=
B
s
0
0
¯
B
s
1
=
B
s
1
0
,
¯
B
s
=
0 B
s
2
I 0
,
¯
C
s
=
0 I
C
s
2
0
¯
C
s
0
=
C
s
0
0
,
¯
C
s
1
=
C
s
0
0
,
¯
D
s
20
=
0
D
s
20
¯
D
s
21
=
0
D
s
21
,
¯
D
s
02
=
0 D
s
02
,
¯
D
s
12
=
0 D
s
12
.
The objective of this paper is to design a single output
feedback controller (3), which can simultaneously stabilize a
finite number of q linear systems (2), and capture additional
H
∞
robustness performance and H
2
control performance.
That is to say, we aim to design a feedback controller such
that every closed-loop system in (4) satisfies the following
requirements:
Requirement 1. For the given constant η
s
> 0, ev-
ery closed-loop system in (4) is asymptotically stable and
satisfies the H
2
performance constraint as
T
ω
s
0
z
s
0
2
<η
s
(5)
where T
ω
s
0
z
s
0
represents the transfer function matrix of the
s-th system (4) from ω
s
0
to z
s
0
.
Requirement 2. For the given constant γ
s
> 0, ev-
ery closed-loop system in (4) is asymptotically stable and
satisfies the H
∞
performance constraint as
T
ω
s
1
z
s
1
∞
<γ
s
(6)
where T
ω
s
1
z
s
1
represents the transfer function matrix of the
s-th system (4) from ω
s
1
to z
s
1
.
3 Analysis of simultaneous H
H
H
2
/H
H
H
∞
∞
∞
sta-
bilization
In this section, we discuss the stability conditions and the
H
2
/H
∞
performance for every closed-loop system in (4). In
order to facilitate our results, we will need Lemma 1.
Lemma 1
[27]
. Let H = H
T
∈ R
n×n
, W and V be real
matrices with appropriate dimensions. Then,
H + W
T
X
T
V + V
T
XW < 0(7)
holds for some X if and only if
(W
⊥
)
T
H(W
⊥
) < 0
(V
⊥
)
T
H(V
⊥
) < 0. (8)
Note that if W or V has rank n, the first or second inequal-
ity will disappear.
3.1 A novel expression of the simultaneous
H
H
H
2
stabilization problem
In order to make sure that the H
2
performance and the
H
∞
performance can be unified into a framework, we need
to develop a new technique and derive a necessary and suffi-
cient condition for the simultaneous H
2
stabilization prob-
lem.
Theorem 1. Assuming that D
s
cl0
= 0, the following
statements are equivalent:
1) Every closed-loop system in (4) is asymptotically sta-
ble and satisfies
T
ω
s
0
z
s
0
2
<η
s
.
2) For some given constant η
s
> 0, there exist X
s
> 0,
Z
s
> 0 satisfying
X
s
(A
s
cl
)
T
+(A
s
cl
)X
s
#
C
s
cl0
X
s
−I
< 0(9)
−Z
s
#
B
s
cl0
−X
s
< 0, tr(Z
s
) < (η
s
)
2
. (10)
3) Given some constant η
s
> 0, there exist X
s
> 0,
Z
s
> 0, an arbitrary F>0, and a large scalar α>0
satisfying (10) and the following inequality (11), for each