494 IEEE TRANSACTIONS ON AUTOMATION SCIENCE AND ENGINEERING, VOL. 15, NO. 2, APRIL 2018
information flow topology is network formation. The dynamic
of the ith vehicle is given by
˙x
i
(t) = (A + A
i
)x
i
(t) + Cf(x
i
(t), t) + Bu
i
(t) (1)
where x
i
(t) ∈ R
n
is the state of the ith vehicle, u
i
(t) ∈ R
m
is
a consensus protocol to be designed, m, n ∈ N, f (x
i
(t), t) =
( f
1
(x
i
(t), t),..., f
n
(x
i
(t), t))
T
, i = 1,...,N, f (·) : R
n
×
[0, +∞) → R
m
is a continuously differentiable vector-valued
function representing the intrinsic nonlinear dynamics of the
ith agent, A and B are two constant real matrices, and A
i
is
a time-varying state-dependent uncertainty of vehicle i.
The following assumptions are introduced in this paper.
Assumption 1: The system matrix pair (A, B) is
stabilizable.
Assumption 2: For any i ∈{1,...,N}, there exist a positive
constant ρ and a matrix E
i
: R
+
→ R
n×n
,sothat
A
i
(t) = ρ AE
i
(t), E
i
(t)
E
i
(t) ≤ I
n
. (2)
Assumption 3: There exists a matrix , such that
| f (y, t) − f (x, t)|≤|y − z|, ∀y, z ∈ R
n
, t ≥ 0. (3)
Remark 1: Note that Assumption 2 is a condition of the
time-varying state-dependent uncertainty of the ith vehicle, in
which the positive constant ρ is a bounded constraint constant.
The similar assumption can be found in [50]. In addition,
Assumption 3 is a Lipschitz condition, in which the matrix
is Lipschitz constraint constant. The similar assumption can
be found in [19].
This paper addresses the leader–follower consensus prob-
lem for multivehicle wirelessly networked uncertain systems
with discontinuous communication due to packet loss or
temporary actuator failure [51]–[53]. Under such scenarios,
the leader–follower consensus protocol is designed by a dis-
tributed intermittent communication strategy. To analyze the
effects of actuator faults, actuator behaviors of the agents
are divided into normal, loss of effectiveness, and miss and
outage communication. For convergence analysis, it is further
assumed that these three types of actuator behaviors exist in
an execution cycle. Moreover, we assume that the vehicles
have the same actuator fault behavior, i.e., the actuators of
all vehicles occur, the component degradation or outage.
Let F be the actuator fault mode, and u
F
i,i
in
,r
be the input
signal of the i
in
th actuator with the rth fault mode. Then, the
actuator fault mode of the i agent is given by
u
F
i,i
in
,r
(t) = η
r
i,i
in
u
i
(t) (4)
where i
in
= 1,...,m, r = 1,...,L, η
r
i,i
in
∈[η
r
i
in
, η
r
i
in
] is a
bounded constant, index r denotes the rth fault mode, L is the
number of total fault modes, and m is the number of actuators
of the ith vehicle. In real applications, we have 0 ≤ η
r
i,i
in
≤
η
r
i,i
in
≤ η
r
i,i
in
. Note that the normal behavior implies η
r
i,i
in
=
η
r
i,i
in
= 1, which means no fault in the i
in
th actuator of the
i-vehicle and u
F
i,i
in
,r
(t) = u
i
(t); the miss and outage behavior
implies η
r
i,i
in
= η
r
i,i
in
= 0, which means that the i
in
th actuator
of the i-vehicle is miss and outage in the rth fault mode and
u
F
i,i
in
,r
(t) = 0; the loss of effectiveness behavior implies 0 <
η
r
i,i
in
< η
r
i,i
in
< 1, which means the partial degradation of
TABLE I
A
CTUATOR FAULT MODE
the i
in
th actuator of the i-vehicle with the rth fault mode and
u
F
i,i
in
,r
(t) = η
r
i,i
in
u
i
(t). Table I summarizes the fault mode for
multivehicle wirelessly networked systems.
Denote u
F
i,r
(t) = (u
F
i,1
in
,r
(t),...,u
F
i,m
in
,r
(t))
T
= η
r
i
u
i
(t),
where η
r
i
= diag{η
r
1
in
,...,η
r
m
in
}, r = 1,...,L. It can be writ-
ten in a concise form of ∇η
r
={η
r
|η
r
= diag{η
r
1
,...,η
r
N
}}.
Then, the uniform actuator fault model is established for all
possible fault modes L
u
F
(t) = η
r
u(t) (5)
where η
r
∈∇η
r
, r = 1,...,L.
The dynamics of system (1) with actuator fault
model (5) can be described by
˙x
i
(t) = (A + A
i
)x
i
(t) + Cf(x
i
(t), t) + Bη
r
i
u
i
(t). (6)
In this paper, we assume that the leader vehicle plays the
role of a command generator and provides reference states that
have to be approached by the followers. That is, the leader
(indexed by 1) evolves without being affected by the follower
vehicles, i.e., u
1
(t) ≡ 0 in (6). The control objective here is to
design a distributed leader–follower consensus algorithm based
on the limited information of local neighbors, such that the
states of followers asymptotically track the reference states of
the leader vehicle, which is mathematically defined as follows.
Definition 2: The leader–follower consensus of (6) is
achieved if and only if the following condition holds for any
initial conditions:
lim
t→∞
x
i
(t) − x
1
(t)=0(7)
where x
1
(t) is the state of the leader vehicle.
Before moving on, we define a switching signal
σ(t) :
[0, +∞) →{1,...,s}, in which each
σ(t) is a possi-
ble directed topology that corresponds to a specific actu-
ator fault mode. Without loss of generality, let G
σ(t)
be
the topology of system (6) for t ≥ 0. Suppose that
there exists an infinite sequence of uniformly bounded
nonoverlapping time interval t ∈[
ˆ
t
k
,
ˆ
t
k+1
) with
ˆ
t
1
= 0,
ν
1
>
ˆ
t
k+1
−
ˆ
t
k
≥ ν
0
> 0. Furthermore, suppose that there
exists an infinite but bounded sequence of fault time intervals
[
¯
t
p
,
¯
t
p
+ ρ
p
) with
¯
t
1
> 0,
¯
t
p+1
>(
¯
t
p
+ ρ
p
) and ρ
p
> 0,
p ∈ N, indicating the actuator is loss of effectiveness in
t ∈∪
p∈N
[
¯
t
p
,
¯
t
p
+ρ
p
). Suppose that there exists an infinite but
bounded sequence of disconnected time intervals t ∈[
¯
t
q
,
¯
t
q
+
ρ
q
) with
¯
t
1
> 0,
¯
t
q+1
>
¯
t
q
+ρ
q
and ρ
q
> 0, q ∈ N, indicating
the actuator is miss and outage in t ∈∪
q∈N
[
¯
t
q
,
¯
t
q
+ ρ
q
).
Based on the above-mentioned statements, there exists an
infinite but bounded sequence of nonoverlapping time intervals
[t
k
, t
k+1
) with t
1
= 0, k ∈ N, such that there exist positive