Dynamics of Linear Switched Systems with Disturbances
Xingwen Liu
1
, Member, IEEE
1. College of Electrical and Information Engineering, Southwest University for Nationalities of China, Chengdu, Sichuan, 610041,
China
E-mail: xingwenliu@gmail.com
Abstract: This paper addresses the dynamics of discrete-time linear switched systems subject to disturbances. The
considered systems are with time-varying delays. It is assumed that the nominal systems are exponentially stable and
the disturbances satisfy vanishing condition plus one of the following three constraints: Being locally Lipschitz at origin,
globally Lipschitz, and differentiable at origin. By “vanishing”, we mean that the disturbance is zero at origin. It is shown
that, with these assumptions, the disturbed system is locally exponentially stable if the disturbance is locally Lipschitz at
origin or differentiable at origin, is globally stable if the disturbance is globally Lipschitz.
Key Words: Delays, exponential stability, disturbances, linear switched systems.
1 INTRODUCTION
As an important class of hybrid dynamic systems, switched
systems inherit the feature of both continuous state and dis-
crete state dynamic systems. Loosely speaking, a switched
system consists of a family of dynamical subsystems and a
rule, called a switching signal, that determines the switch-
ing manner between the subsystems. Many dynamic sys-
tems can be modeled as switched systems [1, 2] which pos-
sess rich dynamics due to the multiple subsystems and vari-
ous possible switching signals [3, 4]. It has been witnessed
that increasing attention has been paid to switched systems
and that great improvements have been made [5–7], how-
ever, there are still many unsolved and challenging issues
[8].
Stability is one of the most important properties of a dy-
namic system and has been extensively investigated in var-
ious areas. Without exception, a number of different sta-
bility properties of switched systems have attracted a great
deal of attention from researchers in this field, see see [9–
14] for details.
Any system in the real world is subject to certain distur-
bance which results in performance deterioration and sys-
tem’s malfunction [15, 16]. There are different methods
to analyze and synthesize a system subject to disturbances.
The frequently used methods include H
∞
, H
2
approach-
es [17–22], and so on. The concept of the input-to-state
stability describes how the state of a disturbed system is
affected by external disturbance [23–27]. In the situations
above-mentioned, the norms of disturbances are generally
upper bounded, but do not possess the “vanishing” proper-
ty. By “vanishing”, we mean that the disturbance is zero if
This work was partially supported by National Nature Science
Foundation (61273007), Sichuan Youth Science and Technology Fund
(2011JQ0011), the Key Project of Chinese Ministry of Education
(212203), SWUN Construction Projects for Graduate Degree Programs
(2014XWD-S0805), SWUN Innovation Teams (14CXTD03), and SWUN
Fundamental Research Funds for Central Universities (12NZYTH01,
2012NZD001, 12NZYQN17).
the state is zero. Recently, it was revealed in [28, 29] that,
with the assumption that the nominal system is exponen-
tially stable, the disturbed system has a dynamics similar
to decaying disturbance.
In the present paper, we deal with the stability property in
the sense of Lyapunov of disturbed systems. It is assumed
that the nominal system is exponentially stable and the dis-
turbance is vanishing. With the same assumption, it was
shown that the disturbed system is still exponentially sta-
ble if the disturbance is small enough [30]. A natural ques-
tion arises: Does such a conclusion hold for systems with
delays, especially with time-varying delays? Unfortunate-
ly, up to now, the expected conclusion has not appeared in
literature. On this ground, we will discuss the properties
of systems with time-varying delays with two assumptions
above-mentioned. However, completely solving this prob-
lem is rather difficult, thus we confine ourselves to the case
of linear switched systems with time-varying delays.
The main contribution of the paper lies in the following
aspects: First, a series of lemmas is presented, these lam-
mas form the basis of our main results and can be applied
to other systems in the future. Second, robust exponential
stability of disturbed systems is analyzed, three kinds of
vanishing disturbances are involved: Locally Lipschitz at
origin, globally Lipschitz, and differentiable at origin with
differentiation zero. For each case, it is shown that if the
disturbance is sufficiently small, then the disturbed system
is locally exponentially stable or globally exponentially sta-
ble, depending on the property of disturbance.
The rest of this paper is organized as follows. Preliminaries
are presented in Section 2, main results are proposed in
Sections 3. Finally, Section 4 concludes this paper.
Notation: A
T
is the transpose of matrix A, and I is the unit
matrix of appropriate dimension. R
n
is the n-dimensional
real vector space. R
n×m
denotes the set of all real ma-
trices of n × m-dimension. N
0
denotes the set of non-
negative integers and N = N
0
\{0}. For any m ∈ N,
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c
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