Mathematical Problems in Engineering
When ∈
𝑙
𝑘
𝑘
,thestateerror(
𝑘
)is dened as
𝑘
=
𝑘
−
𝑘
.
()
When ∈
𝑙
𝑘
𝑘
, based on the combinations of (), (),
and () and the combinations of (), (),and(),we,
respectively, obtain
𝑇
𝑘
Φ
1
𝑘
≤
𝑇
(
−
(
))
Φ
2
(
−
(
))
,
()
𝑇
𝑘
Φ
𝑘
≤
𝑇
(
−
(
))
Φ
(
−
(
))
.
()
Based on the combination of (), (),and(), ()is also
written as
(
)
=
𝑟
𝑗=1
𝑗
(
(
))
𝑗
(
−
(
))
−
𝑘
.
()
In consideration of general actuator failures [], the
model of control input with actuator failure is described as
𝑓
(
)
=
(
)
.
()
Matrix denotes the mode set of system actuator failures
and describes the fault extent, where =diag{
1
,...,
𝑚
},
𝑞
∈[0,1], =1,2,...,;
𝑞
=0 indicates that the th system
actuator is invalid;
𝑞
∈(0,1) implies that the th system
actuator is at fault to some extent; and
𝑞
= 1 denotes that
the th system actuator operates properly.
rough the combination of (), (),and(),the
nonlinear networked closed-loop fault systems (NNCFSs)
model with actuator saturation constraints can be obtained
basedontheDETCSasfollows:
(
)
=
𝑟
𝑖=1
𝑟
𝑗=1
𝑖
+
𝑖
(
)
+
𝑖
+
𝑖
sat
𝑗
(
−
(
))
−
𝑘
,
()
where ∈
𝑙
𝑘
𝑘
and the initial state ()is denoted by Ψ(),
where ∈[−
2
,0]. Meanwhile, set Ψ(0)as
0
,whereΨ()is a
continuous function in the interval [−
2
,0].
Remark 1. e NNCSs model integrates many factors into a
unied framework. ese factors include the communication
constraint condition, network time delay, actuator saturation,
actuator failures, and the control law. e model lays a solid
foundation for the following codesign of communication
parameters and fault-tolerant controller for NNCSs.
2.2. Related Denition and Lemma. Before commencing the
proof of the theorem, we present several related denitions
and lemmas.
Denition 2. If the of -stability is dened as the system
stability margin for a system without failure, then the of
-stability can be extended as the system safety margin for
a system with any possible actuator failures in mode set ;
the system safety margin can also be abbreviated as -safety
degree. e denition indicates that all the closed-loop poles
of system
𝑖
(=1,2,...,)satisfy Re(
𝑖
)<−and >0for
the system with any possible actuator failures in mode set .
Denition 3. In the process of state transformation, if the
following conditions are satised for the system with any
possible actuator failures in mode set ,
() the system possesses -safety degree,
() the state trajectory whose initial state is from any
point of set
𝑛
will converge to the equilibrium point;
namely
℘
𝑎1
=
0
∈
𝑛
: lim
𝑡→∞
,
0
=0,∀; ()
then ℘
𝑎1
is dened as fault-tolerant domain of
attraction with -safety degree, where (,
0
)is the
corresponding state trajectory.
Denition 4. In the process of state transformation, if the
following conditions are satised for system with any possible
actuator failures in mode set ,
() the system possesses -safety degree,
() the state trajectory, the initial state of which is from
any point of set ℘
𝛼2
, remains inside the set ℘
𝛼2
,
0
∈℘
𝛼2
⇒
(
)
∈℘
𝛼2
,∀≥0,.
()
() the state trajectory, the initial state of which is from
any point of set ℘
𝛼2
\{0},convergestotheequilibrium
point,
0
∈℘
𝛼2
\
{
0
}
⇒ lim
𝑡→∞
,
0
=0,∀,
()
then ℘
𝛼2
is the contractively invariant set of fault
tolerance with -safety degree, where (,
0
)is the
corresponding state trajectory.
e contractively invariant set of fault tolerance with -
safety degree is within the fault-tolerant domain of attraction
with -safety degree. In general, obtaining the corresponding
fault-tolerant domain of attraction is dicult; thus, the
fault-tolerant domain of attraction with -safety degree can
be estimated in terms of the corresponding contractively
invariant set of fault tolerance.
If () = {
0
∈
𝑛
:|
𝑙
|≤1,=1,2,...,},where
matrix ∈
𝑚×𝑛
and
𝑙
denotes the th row of matrix ,then
()is dened as the region where the feedback control =
sat()is linear for , as indicated in [].
Basedonanellipsoidestimationofthedomainofattrac-
tion, ∈
𝑛×𝑛
is a positive denite matrix. For >0, the
ellipsoid is dened as (,)={∈
𝑛
,
𝑇
≤ },where
()denotes (,1).
Lemma 5 (see []). Given two feedback matrices ∈
𝑚×𝑛
and ∈
𝑚×𝑛
,if∈(),then
sat
(
)
∈co Υ
𝑖
+Υ
−
𝑖
:=1,2,...,2
𝑚
,
()
where {⋅} denotes the convex hull of the linear feedback
control group Υ
𝑖
+Υ
−
𝑖
, Υ
𝑖
∈Υ, =1,...,2
𝑚
; Υdenotes
the set of ×diagonal matrices whose diagonal elements