Observer-based consensus of second-order multi-agent systems
without velocity measurements
Chenglin Wen
a
, Fang Liu
b
, Qiang Song
a,
n
, Xiaoliang Feng
a
a
College of Electrical Engineering, Henan University of Technology, Zhengzhou 450001, China
b
School of Information Engineering, Huanghuai University, Zhumadian, Henan 463000, China
article info
Article history:
Received 2 September 2015
Received in revised form
24 October 2015
Accepted 27 November 2015
Communicated by Guang Wu Zheng
Available online 17 December 2015
Keywords:
Second-order consensus
Multi-agent system
Distributed observer
Double integrator
Harmonic oscillator
Time delay
abstract
This paper investigates the consensus of second-order multi-agent systems without measuring the
velocity states of the agents, where each agent can be either a double integrator or a harmonic oscillator.
By utilizing the position information of the agents, a distributed observer-based protocol is proposed to
solve the second-order consensus problem of multi-agent systems with or without time delay. The
observer-based consensus problem is converted to the stability analysis for a set of second-order quasi-
polynomials through coordinate transform and system decomposition. Then, some necessary and suf-
ficient conditions are derived for reaching second-order consensus in multi-agent systems with or
without time delay, respectively, and it is shown that the consensus can be achieved if and only if the
communication delay is less than a critical value. Simulation examples are given to verify the theoretical
analysis.
& 2015 Elsevier B.V. All rights reserved.
1. Introduction
In the past few decades, the consensus problem has been a
focal point of many different disciplines due to its important role
in the investigation of the distributed coordination of multi-agent
systems. The consensus in a multi-agent system is said to be
reached if all the agents can eventually agree on some common
value under some control algorithms based on local information.
Much progress has been made in the consensus of multi-agent
systems with first-order dynamics [1–3], second-order dynamics
[4–9], higher-order dynamics [10–13] and fractional-order
dynamics [14,15]. In particular, much effort has been devoted to
the second-order consensus problem due to many practical
applications of second-order multi-agent systems, such as the
flocking of unmanned air vehicles [16,17] and the formation con-
trol of multiple mobile robots [18,19]. It is worth mentioning that
the first-order consensus problem is closely related to the syn-
chronization problem of complex networks [20–23].
A second-order linear multi-agent system is composed of a set
of interconnected systems, where each agent may be a double
integrator [4–6], a spring-mass system [24], or a harmonic oscil-
lator [25,26]. Moreover, it is worth mentioning that a harmonic
oscillator and a double integrator can be described by a unified
mathematical model. Some fundamental results have been
obtained to address the second-order consensus of multi-agent
systems with double-integrator dynamics [4–6]. In recent years,
the consensus problem of coupled harmonic oscillators has been
intensively investigated by using many different control strategies
[25–29]. It is now well known that the existence of a directed
spanning tree in network topology is a necessary condition for
reaching second-order consensus [4], and both the real and ima-
ginary parts of the nonzero eigenvalues of network Laplacian
matrix are important to discuss the consensus problem [5].
Since the time delay is inevitable in many physical systems
[30–32], some researchers have studied the consensus in a net-
work of double integrators or harmonic oscillators with time
delay. For coupled double-integrators, Yu et al. [5] showed that the
communication delay should be less than some critical value and
Meng et al. [6] further analyzed the effects of input and commu-
nication delays on second-order consensus. As for coupled har-
monic oscillators, Zhang et al. [27] considered the consensus in the
network with delayed velocity coupling, while Song et al. [29]
investigated the consensus using delayed position information and
proved that the time delay should be chosen from a set of bounded
intervals.
Note that most consensus protocols for coupled double inte-
grators [4–6] and coupled harmonic oscillators all require velocity
states [25–28]. However, for a second-order multi-agent system
without being equipped with velocity sensors, the velocity infor-
mation will not be available. Moreover, in some practical cases, the
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/neucom
Neurocomputing
http://dx.doi.org/10.1016/j.neucom.2015.11.087
0925-2312/& 2015 Elsevier B.V. All rights reserved.
n
Corresponding author.
E-mail address: qsongseu@gmail.com (Q. Song).
Neurocomputing 179 (2016) 298–306