Adaptive Mittag-Leffler stabilization of commensurate fractional-order
nonlinear systems
Dongsheng Ding, Donglian Qi, Yao Meng and Li Xu
Abstract— In this paper, a new adaptive control technique
called adaptive fractional-order backstepping is proposed, for a
class of commensurate fractional-order nonlinear systems with
uncertain constant parameters. Using the adaptive fractional-
order backstepping as a basic design tool, we show how to
explicitly construct an adaptive feedback control laws that
solve the Mittag-Leffler stabilization problem of uncertain
commensurate fractional-order nonlinear systems. The global
convergence of the closed-loop systems is guaranteed in the
sense of Mittag-Leffler stability. The efficiency of the proposed
technique is demonstrated in simulation finally.
I. INTRODUCTION
Currently, fractional-order systems have been widely used
in the area of dynamical systems and control. This is mainly
due to that many physical systems are well characterized
by fractional-order differential equations [1]–[3], such as
ultracapacitor, viscoelastic mechanical system and diffusive
system, etc. For more details on this area, one can refer to
the monographs [1]–[4], the papers [5]–[20], [22]–[28] and
the reference therein.
Uncertainties are common phenomena in all dynamical
systems including fractional-order systems. Recently, many
results are devoted to cope with uncertainties in fractional-
order systems. By use of linear matrix inequality (LMI)
technique, several works concentrated on robust stabilization
of uncertain fractional-order systems. The LMI-based robust
stabilization conditions of uncertain fractional-order linear
systems were proposed in [5]–[7] early. For some recent
works, one can refer to [8]–[10] and the references therein.
Besides, H
∞
control problems of fractional-order systems
were investigated in [11]–[13] recently. For some noises
that appear in processes or in measurements, [14] proposed
self-tuning control for stochastic fractional-order systems.
However, initially uncertain (or time-varying) parameters
always exist in fractional-order systems. Adaptive control
was famous to deal with them, which has been introduced for
fractional-order systems. By extending the classical model
reference adaptive control (MRAC), fractional-order refer-
ence model or adaptive laws shown in [15]–[18] and the
references therein. Another important method is fractional-
order sliding mode control, which were presented in [19],
[20] and the references therein for uncertain fractional-order
linear or nonlinear systems.
This work was supported by the National Natural Science Foundation
of China under Grant 61171034 and the Province Natural Science Fund of
Zhejiang under Grant R1110443.
The authors are with College of Electrical Engineering, Zhejiang Univer-
sity, Hangzhou 310027, China. donsding@126.com
As we know, adaptive backstepping is a well-known
technique of stabilizing uncertain nonlinear systems with
unknown constant parameters [21]. However, to the authors’
best knowledge, this technique is restricted to the classical
uncertain integer-order nonlinear systems. There few results
on uncertain fractional-order nonlinear systems stabiliza-
tion via adaptive backstepping. Motivated by the mentioned
developments, we devote to solve the Mittag-Leffler sta-
bilization problem of uncertain fractional-order nonlinear
systems via adaptive backstepping. As the resulting adaptive
control laws are with fractional-order forms, we call such
methodology the adaptive fractional-order backstepping.
An attention should be paid to, Mittag-Leffler stability just
describes the pseudo-state trajectories, not the real states of
fractional-order systems, which you can refer to references
[22]–[24] for distinguishing them. So, we call the Lyapunov
function construction for Mittag-Leffler stability as fractional
Lyapunov function, which cannot be seen as energy-like
functions as asserted in [24], [25].
In our contributions, the Mittag-Leffler stabilization prob-
lem of uncertain commensurate fractional-order nonlinear
systems is solved with a guaranteed global convergence
of closed-loop systems. Firstly a general framework of
Lyapunov-like based design is well defined via adaptive
control fractional Lyapunov function (acflf) for fractional-
order systems. Within this framework, adaptive fractional-
order backstepping is proposed by extending the classical
adaptive backstepping for uncertain fractional-order non-
linear systems. The analytic forms of adaptive feedback
control laws are designed via the adaptive fractional-order
backstepping. The proposed technique is verified finally in
an application.
The paper is organized as follows. In Section II, some
definitions and the concept of acflf are introduced. In Section
III, fractional-order backstepping is reviewed firstly. By
extending it, the adaptive fractional-order backstepping is
concluded by stabilizing uncertain fractional-order nonlinear
systems. The analytic forms of adaptive feedback control
laws are derived. The theoretical result is verified in Section
IV. Finally, we conclude the paper in Section V.
II. PRELIMINARIES
The Caputo fractional-order derivative is used.
Definition 2.1: [4] Let f (t) is a real continuously dif-
ferentiable function. The Caputo fractional-order derivative
with order 0 <
ν
< 1 on t > 0 is defined by
D
ν
t
f (t) =
1
Γ(n −
ν
)
Z
t
0
f
(n)
(
τ
)
(t −
τ
)
ν
−n+1
d
τ
,
53rd IEEE Conference on Decision and Control
December 15-17, 2014. Los Angeles, California, USA
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