Chinese Journal of Electronics
Vol.23, No.2, Apr. 2014
Dynamics of a Strengthened Chaotic System and
Its Circuit Implementation
∗
SUN Kehui, LIU Xuan and ZHU Congxu
(School of Physics and Electronics, Central South University, Changsha 410083, China)
Abstract — To strengthen a chaotic system, a state
feedback controller is applied to generate hyperchaotic be-
haviors based on the simplified Lorenz system, and a co-
ordinate transformation is used for converting topologi-
cal structure of the hyperchaotic system from two wings
to four wings. Complex dynamics of the hyperchaotic
and four-wing attractor system are analyzed and verified
by Lyapunov exponent spectrums, bifurcation diagrams,
phase portraits, Poincar´e sections and circuit realization.
The circuit experiment results are agreed well with the
simulation results, and it lays a good foundation for the
chaotic secure communication.
Key words — Hyperchaos, Multi-wing attractor, Sim-
plified Lorenz system, Circuit implementation.
I. Introduction
With developing of chaos secure communication technolo-
gies
[1]
, more complicate chaotic systems are required to im-
prove the performances of chaotic application systems. It also
is the purpose of chaotic anti-controlling. In other words, we
call it the strengthening of chaos in this paper. It involves
the problems of increasing system complexity and structural
complexity. On one hand, hyperchaos characterized with more
than one positive Lyapunov exponent, is more complicate than
general chaos. There are some approaches to generate hy-
perchaos, such as state feedback
[2]
, time delayed feedback
[3]
,
multi-system couple
[4]
, external forcing function
[5]
, switching
control
[6,7]
, and special designed functions
[8−10]
.Amongthese
approaches, the state feedback control is the simplest one and
easy to implement in the practice. On the other hand, a sys-
tem with multi-wing or multi-scroll attractor is more compli-
cate than that with a single wing or double wing attractor.
In the past three decades, based on Chua system and Lorenz
system, people explored many methods to increase wings or
scrolls for a chaos attractor
[11−16]
, and proved that the com-
plex multi-scroll chaotic attractors have potential engineering
applications in various chaos-based technologies and informa-
tion systems
[17]
. For the Lorenz system family, people usually
employ function method to transform the structure of differen-
tial equations
[15]
, which produce three or four wings attractor.
Recently, a new approach for generating four-wing chaotic sys-
tem was proposed, via a mathematical transformation
[18]
.It
can preserve the properties of the original system and increase
the number of wings at the same time. In 2009, a simplified
Lorenz system with one parameter was reported in Ref.[19],
which has abundant dynamical behaviors, and it is another
ideal candidate system for chaos applications. In this paper,
we focus on the dynamics and circuit implementation
[20]
of the
strengthened simplified Lorenz chaotic system. It is organized
as follows. In Section II, a state feedback controller is applied
to the simplified Lorenz system to generate hyperchaos. In
Section III, the coordination transformation is applied to the
hyperchaotic simplified Lorenz systems to get the four-wing
attractors. In Section IV, the circuit implementation of the
four-wing hyperchaotic system is presented. Finally, we sum-
marize the results and indicate future directions.
II. Generating Hyperchaos via a State
Feedback Controller
The simplified Lorenz system with a single parameter c is
described by
[20]
⎧
⎪
⎨
⎪
⎩
˙x = 10(y − x)
˙y =(24− 4c)x − xz + cy
˙z = xy − 8z/3
(1)
where x, y,andz are state variables. When c ∈ (−1.59, 7.75),
the system is chaotic. To construct a hyperchaotic system, a
state feedback controller u = −kx is designed to the system
Eq.(1), where k is the feedback coefficient. The new modified
system has the form of
⎧
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎩
˙x = 10(y − x)
˙y =(24− 4c)x − xz + cy + u
˙z = xy − 8z/3
˙u = −kx
(2)
Since the system Eq.(2) is a four-dimensional autonomous sys-
tem, it will have four Lyapunov exponents thereby getting a
chance to be hyperchaotic. Considering c = −1, the Lyapunov
exponent spectrum versus k and the corresponding bifurcation
diagrams are obtained as shown in Fig.1. It was observed that
∗
Manuscript Received Sept. 2011; Accepted May 2012. This work is supported by the National Natural Science Foundation of China
(No.61161006 and No.61073187), and the SRF for ROCS, SEM.