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具有切换交互拓扑的高阶线性群系统的时变编队控制
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研究了具有切换相互作用拓扑的高阶线性时不变群系统的时变编队控制问题。首先提出了一种通用的编队控制协议。然后使用基于共识的方法,提出了具有切换交互拓扑的群体系统实现给定时变形式的充要条件。给出了时变地层参考函数的显式表达式。结果表明,切换交互拓扑结构对编队参考功能没有影响,可以指定编队参考的运动模式。此外,提出了形成可行性的必要条件和充分条件。给出了一种扩展可行编队集的方法,并提供了一种算法,用于设计具有切换交互拓扑的群体系统的协议以实现时变编队。最后,数值模拟被提出来证明理论结果。
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www.ietdl.org
Published in IET Control Theory and Applications
Received on 11th November 2013
Revised on 16th March 2014
Accepted on 18th March 2014
doi: 10.1049/iet-cta.2013.1007
Special Issue on Recent Developments in
Networked Control and Estimation
ISSN 1751-8644
Time-varying formation control for high-order linear
swarm systems with switching interaction topologies
Xiwang Dong, Zongying Shi, Geng Lu,Yisheng Zhong
Department of Automation,TNlist,Tsinghua University, Beijing 100084, People’s Republic of China
E-mail: szy@mail.tsinghua.edu.cn
Abstract: Time-varying formation control problems for high-order linear time-invariant swarm systems with switching inter-
action topologies are investigated. A general formation control protocol is proposed firstly. Then using a consensus based
approach, necessary and sufficient conditions for swarm systems with switching interaction topologies to achieve a given
time-varying formation are presented. An explicit expression of the time-varying formation reference function is given. It is
revealed that the switching interaction topologies have no effect on the formation reference function and the motion modes
of the formation reference can be specified. Furthermore, necessary and sufficient conditions for formation feasibility are
presented. An approach to expand the feasible formation set is given and an algorithm to design the protocol for swarm
systems with switching interaction topologies to achieve time-varying formations is provided. Finally, numerical simulations
are presented to demonstrate theoretical results.
1 Introduction
Recently, formation control of swarm systems has attracted
considerable attention because of its broad potential appli-
cations in civilian and military areas such as load trans-
portation [1], radiation detection and contour mapping
[2], target search and localisation [3], reconnaissance [4],
surveillance [5], telecommunication relay [6] and so on.
In the past decades, several formation control approaches
have been proposed in the robotics community, such as
behaviour [7], leader-follower [8] and virtual structure [9]
based approaches and so on. However, Beard et al.[10]
pointed out that behaviour, leader-follower and virtual struc-
ture based formation control approaches have their own
weaknesses. For example, behaviour based approaches are
difficult to be analysed mathematically, and leader-follower
approaches lack of robustness because of the existence of
the leader, just to name a few.
In recent years, consensus for linear time-invariant (LTI)
swarm systems have been studied extensively (see, e.g.
[11–18] and references therein). With the development of
consensus theory, more and more researchers find that con-
sensus approaches can be used to deal with formation control
problems. Using consensus based approaches, Ren [19] dis-
cussed formation control problems for second-order swarm
systems, and revealed that behaviour, leader-follower and
virtual structure based approaches can be treated as special
cases of consensus based approaches and the weaknesses of
the these approaches can be overcome. In [20], a consensus
based formation control strategy was applied to a multi-robot
swarm system. Xiao and Wang [21] investigated finite-time
formation control problems for first-order swarm systems
based on consensus approaches. Sufficient conditions for
second-order swarm systems with undirected interaction
topologies to achieve formations were presented in [22].
Consensus based formation control problems for second-
order swarm systems with time delays were addressed in
[23]. Chen et al.[24] discussed formation control prob-
lems for first-order and second swarm systems with bounded
input, disturbance and time delays.
In practical applications, many swarm systems are of high
order, so formation control problems for high-order swarm
systems make more sense. Based on consensus approaches,
Lafferriere et al.[25] proposed a necessary and sufficient
condition for swarm systems with a special high-order LTI
model, which can be regarded as a series of second-order
models, to achieve formations. Fax and Murray [26] dis-
cussed formation stability problems for general high-order
LTI swarm systems. Formation stability problems for gen-
eral high-order LTI swarm systems with fixed and periodic
switching undirected interaction topologies were studied in
Porfiri et al.[27]. However, both Fax and Murray [26] and
Porfiri et al.[27] only considered formation stability prob-
lems and did not consider the formation feasibility problems.
For a swarm system, whether or not a given formation is
feasible is a crucial problem. For general high-order LTI
swarm systems, Ma and Zhang [28] proposed a necessary
and sufficient condition for formation feasibility. However,
the formation considered in [28] is time-invariant and the
feasible formation set is very limited. Moreover, the inter-
action topologies in [28] are assumed to be fixed. In practical
applications, the interaction topologies may be switching
because of the existing of interaction channel failures and
creations among agents. When interaction topologies are
switching, both the analysis and design for cooperative
control of swarm systems become much complicated and
2162 IET Control Theory Appl., 2014, Vol. 8, Iss. 18, pp. 2162–2170
© The Institution of Engineering and Technology 2014 doi: 10.1049/iet-cta.2013.1007
www.ietdl.org
challenging than the fixed case [29]. To the best of our
knowledge, time-varying formation analysis and feasibility
problems for general high-order LTI swarm systems with
switching interaction topologies have not been investigated.
In this paper, time-varying formation control problems
for general high-order LTI swarm systems with switching
interaction topologies are dealt with. Firstly, a consensus
based formation protocol is presented. Then the formation
problems are transformed into consensus problems. Nec-
essary and sufficient conditions for high-order LTI swarm
systems with switching interaction topologies to achieve
time-varying formation are proposed. An explicit expression
of the time-varying formation reference function is given,
and it is shown that switching interaction topologies have
no effect on the formation reference function and the motion
modes of the formation reference can be assigned. More-
over, necessary and sufficient conditions for time-varying
formation feasibility are presented, where the feasible for-
mation set can be expanded. Finally, an algorithm to design
the protocol for swarm systems with switching interaction
topologies to achieve time-varying formation is proposed.
Compared with the existing works on formation control,
the novel features of the current paper are threefold. Firstly,
both formation analysis and feasibility problems for general
high-order LTI swarm systems with switching interaction
topologies are discussed. In [19–27], formation feasibility
problems were not considered. The interaction topologies in
[28] were fixed. In [19–24], the dynamics of each agent is
restricted to be low-order. Secondly, the formation can be
time-varying whereas the formations in [25–28] are time-
invariant, and a description of the feasible formation set
is also shown. Thirdly, an explicit expression of the time-
varying formation reference function is given, and it is
shown that the motion modes of the formation reference
can be specified. Moreover, an algorithm to determine the
gain matrices in the protocol is presented. However, protocol
design problems were not dealt with in [26, 27].
The rest of this paper is organised as follows. In Section 2,
basic concepts and useful results on graph theory are intro-
duced and the problem to be investigated is formulated. In
Section 3, necessary and sufficient conditions to achieve
time-varying formation are presented. In Section 4, neces-
sary and sufficient conditions for formation feasibility are
proposed and an algorithm to design the protocol is given.
Numerical simulations are shown in Section 5. Finally,
Section 6 concludes the whole work.
Throughout this paper, for simplicity of notation, let 0
denote zero matrices of appropriate size with zero vectors
and zero number as special cases, and 1
N
be a column vector
of size N with 1 as its elements. Let I
N
represent an identity
matrix with dimension N , and ⊗ denote Kronecker product.
2 Preliminaries and problem description
In this section, basic concepts and results on graph theory
are introduced and the problem description is presented.
2.1 Basic concepts and results on graph theory
An undirected graph G consists of a node set Q =
{
q
1
, q
2
, ..., q
N
}
, an edge set E ⊆
(q
i
, q
j
) : q
i
, q
j
∈ Q, i = j
,
and a symmetric adjacency matrix W =[w
ij
]∈R
N ×N
with
non-negative elements w
ij
.Anedge of G is denoted by
q
ij
= (q
i
, q
j
). The adjacency elements associated with the
edges of G are positive, i.e. w
ji
> 0 if and only if q
ij
∈ E.
Moreover, w
ii
= 0 for all i ∈
{
1, 2, ..., N
}
. The set of neigh-
bours of node q
i
is denoted by N
i
=
q
j
∈ Q : (q
j
, q
i
) ∈ E
.
The in-degree of node q
i
is defined as deg
in
(q
i
) =
N
j=1
w
ij
. The degree matrix of G is denoted by D =
diag
deg
in
(q
i
), i = 1, 2, ..., N
. The Laplacian matrix of G
is defined as L = D − W . An undirected graph is said to
be connected if there is a path from each node to every
other nodes. More details on graph theory can be found in
[30]. The following lemma is useful in analysing formation
problems of swarm systems.
Lemma 1 [30]: Let L ∈ R
N ×N
be the Laplacian matrix of an
undirected graph G, then
(i) L has at least one zero eigenvalue, and 1
N
is the
associated eigenvector; that is, L1
N
= 0; and
(ii) If G is connected, then 0 is a simple eigenvalue of L,
and all the other N − 1 eigenvalues are real and positive.
2.2 Problem description
Consider a swarm system with N agents. Suppose that each
agent has the LTI dynamics described by
˙x
i
(t) = Ax
i
(t) + Bu
i
(t) (1)
where i = 1, 2, ..., N , x
i
(t) ∈ R
n
is the state, u
i
(t) ∈ R
m
is
the control input. The interaction topology of the swarm
system can be described by an undirected graph G, and each
agent can be treated as a node in G. For i, j ∈
{
1, 2, ..., N
}
,
the interaction channel from agent i to agent j is denoted
by the edge q
ij
, and the corresponding interaction strength
is denoted by w
ji
.
Assumption 1: B is of full column rank.
A time-varying formation is specified by a vector h(t) =
[h
T
1
(t), h
T
2
(t), ..., h
T
N
(t)]
T
∈ R
nN
with h
i
(t)(i = 1, 2, ..., N )
piecewise continuously differentiable.
Definition 1: Swarm system (1) is said to achieve
time-varying formation h(t) if there exists a vector-valued
function r(t) ∈ R
n
such that
lim
t→∞
(x
i
(t) − h
i
(t) − r(t)) = 0 (i = 1, 2, ..., N )
where r(t) is called a formation reference function.
Remark 1: The formation definition specified by vectors has
been used a lot in previous works on formation control such
as [19, 20, 22, 24, 25, 27] and so on. Definition 1 presents a
general framework and it can be verified that the definitions
in [19, 20, 22, 24, 25, 27] can be treated as special cases of
Definition 1.
Definition 2: If there exist control inputs u
i
(t)(i = 1,
2, ..., N ) such that swarm system (1) achieves time-varying
formation h(t), then the formation h(t) is feasible for swarm
system (1).
Definition 3: Swarm system (1) is said to achieve consensus
if there exists a vector-valued function c(t) ∈ R
n
such that
lim
t→∞
(x
i
(t) − c(t)) = 0 (i = 1, 2, ..., N )
where c(t) is called a consensus function.
IET Control Theory Appl., 2014, Vol. 8, Iss. 18, pp. 2162–2170 2163
doi: 10.1049/iet-cta.2013.1007 © The Institution of Engineering and Technology 2014
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