ANALYSIS AND SLIDING CONTROLLER DESIGN FOR HYBRID SYNCHRONIZATION OF HYPERCHAOTIC YUJUN SYSTEMS

International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol.3, No.4, August 2013
DOI : 10.5121/ijcsea.2013.3404 39
ANALYSIS AND SLIDING CONTROLLER DESIGN FOR
HYBRID SYNCHRONIZATION OF HYPERCHAOTIC
YUJUN SYSTEMS
Sundarapandian Vaidyanathan
Research and Development Centre, Vel Tech University
Avadi, Chennai-600 062, Tamil Nadu, INDIA
sundarvtu@gmail.com
ABSTRACT
Hybrid synchronization of chaotic systems is a research problem with a goal to synchronize the states of
master and slave chaotic systems in a hybrid manner, namely, their even states are completely
synchronized (CS) and odd states are anti-synchronized. This paper deals with the research problem of
hybrid synchronization of chaotic systems. First, a detailed analysis is made on the qualitative properties of
hyperchaotic Yujun system (2010). Then sliding controller has been derived for the hybrid synchronization
of identical hyperchaotic Yujun systems, which is based on a general hybrid result derived in this paper.
MATLAB simulations have been shown in detail to illustrate the new results derived for the hybrid
synchronization of hyperchaotic Yujun systems. The results are proved using Lyapunov stability theory.
KEYWORDS
Hyperchaotic Yujun System, Hyperchaos, Sliding Control, Synchronization, Lyapunov Stability Theory.
1. INTRODUCTION
By definition, a hyperchaotic system is a chaotic system with more than one positive Lyapunov
exponent which implies that the dynamics can be expanded in several directions.
In 1979, Rössler [1] discovered the hyperchaotic system. Hyperchaotic systems have found many
research applications in neural networks [2], secure communications [3], etc.
In the chaos literature, there has been active interest in developing new methodology for
synchronization of chaotic and hyperchaotic systems.
Some important methods developed for chaos synchronization are OGY method [4], PC method
[5], sampled-data feedback method [6], time-delay feedback method [7], active control method
[8-10], adaptive control method [11-13], backstepping design method [14-15] and sliding mode
control method [16-18].
In this paper, a qualitative analysis has been presented for the 4-D hyperchaotic Yujun system
([19], 2010). Next, a sliding mode controller has been derived for the hybrid synchronization of
identical hyperchaotic Yujun systems.

40
The organization of this paper can be detailed as follows. Section 2 contains general sliding
control results for the hybrid synchronization of master and slave systems. Section 3 describes the
hyperchaotic Yujun system. Section 4 describes the sliding controller design for the hybrid
synchronization of hyperchaotic Yujun systems and MATLAB simulations.
As the drive system, we take the chaotic system
( )x Ax f x= + (1)
where n
x∈R is the system state, A is an n n× constant matrix and : n n
f →R R is the
nonlinear part.
As the response system, we take the identical controlled chaotic system
( )y Ay f y u= + + (2)
where n
y ∈R is the system state and m
u ∈R is the sliding controller to be constructed.
A formal definition of the hybrid synchronization error between the drive system (1) and the
response system (2) can be provided as
, when is an odd integer
, when is an even integer
i i
i
i i
y x i
e
y x i
−
= 
+
(3)
Differentiating (3) and simplifying, we obtain the error dynamics as
( , ) ,e Ae x y u= + + (4)
The design goal is to determine ( )u t so as to drive the error to zero, i.e.
lim ( ) 0
t
e t
→∞
= for each (0) .n
e ∈R (5)
As methodology, we use sliding mode control (SMC) to solve the above design problem.
First, we define the controller u as
( , )u x y Bv= − + (6)
where B is chosen carefully such that ( , )A B is completely controllable.
If we substitute (5) into (4), then the error dynamics takes the simple form
e Ae Bv= + (7)
Eq. (7) represents a single-input linear time-invariant control system.
In SMC control design, we take the sliding variable as
1 1 2 2( ) n ns e Ce c e c e c e= = + + + (8)

41
where [ ]1 2 nC c c c=  is a constant vector to be determined.
In SMC design, the error system (7) is confined to the sliding manifold defined by
{ }| ( ) 0n
S x s e= ∈ =R
The sliding control theory demands that the manifold S be invariant under the flow of (7).
Thus, the error system (7) must satisfy the following two conditions, viz.
( ) 0s e = (9)
and
( ) 0s e = (10)
By making use of Eqns. (7) and (8), Eq. (10) can be simplified in an equivalent form as
[ ]( ) 0s e C Ae Bv= + = (11)
Next, we find the solution v of the equation (11). Thus, we get the equivalent control law
1
eq ( ) ( ) ( )v t CB CA e t−
= − (12)
In Eq. (12), C is selected such that CB is a non-zero scalar.
Plugging in the equivalent control law (12) into (7) yields the simplified dynamics
1
( )e I B CB C Ae−
 = −  (13)
We choose C so that the system matrix 1
( )I B CB C A−
 −  is stable.
It is noted that the resulting system (13) is GAS (globally asymptotically stable).
In our sliding control methodology, to obtain the SMC control for (7), we make use of the
constant plus proportional rate law. This is given by the equation
sgn( )s q s k s= − − (14)
where the gains 0,q > 0k > are constants.
We shall find the gains so that the following hold:
(1) The sliding condition is satisfied.
(2) The sliding motion will occur.
By the use of equations (11) and (14), we get the sliding control ( )v t as

42
[ ]1
( ) ( ) ( ) sgn( )v t CB C kI A e q s−
= − + + (15)
Theorem 1. The drive system (1) and the response system (2), which are identical chaotic
systems, are globally and asymptotically hybrid synchronized for all initial conditions
(0), (0) n
x y R∈ by the sliding control law
( ) ( , ) ( )u t x y Bv t= − + (16)
where ( )v t is given by (15) and B is chosen such that ( , )A B is controllable.
Proof. We prove this theorem by applying Lyapunov stability theory [20].
First, we make a substitution of (16) and (15) into the error system (4).
After this substitution, a simple calculation shows that the error dynamics reduces to
[ ]1
( ) ( ) sgn( )e Ae B CB C kI A e q s−
= − + + (17)
As we prove using Lyapunov stability theory, we have to construct a Lyapunov function for the
error dynamics (17). We consider the following function as a candidate, viz.
21
( ) ( )
2
V e s e= (18)
We note that V is a positive definite function on .n
R
Next, we find the time derivative of V along the trajectories of (16) or the equivalent dynamics
(14). Thus, we obtain
2
( ) ( ) ( ) sgn( )V e s e s e ks q s s= = − −  (19)
We note that V is a negative definite function on .n
R
Hence, the proof is complete by Lyapunov stability theory [20].
3. ANALYSIS OF HYPERCHAOTIC YUJUN SYSTEM
The hyperchaotic Yujun system ([19], 2010) is a four-dimensional system given by
1 2 1 2 3
2 1 2 4 1 3
3 3 1 2
4 4 1 3
( )x a x x x x
x cx x x x x
x bx x x
x rx x x
= − +
= − + −
= − +
= −




(20)
where , , ,a b c r are positive parameters and 1 2 3 4, , ,x x x x are the states of the system.
The system (20) is hyperchaotic when the parameter values are chosen as

43
35, 8 / 3, 55a b c= = = and 1.3r = (21)
When the parameters are given by (21), the system Lyapunov exponents are obtained as
1 2 3 41.4164, 0.5318, 0, 39.1015.L L L L= = = = − (22)
Since there are two positive Lyapunov exponents, the above calculation confirms that the system
(20) is hyperchaotic when the parameter values are given by (21).
The projections of the hyperchaotic Yujun attractor are shown in Figure 1.
Figure 1. The Projections of the Hyperchaotic Yujun Attractor
4. SMC DESIGN FOR HYBRID SYNCHRONIZATION OF HYPERCHAOTIC
YUJUN SYSTEMS
In this section, we take the drive system as the hyperchaotic Yujun system given by
1 2 1 2 3
2 1 2 4 1 3
3 3 1 2
4 4 1 3
( )x a x x x x
x cx x x x x
x bx x x
x rx x x
= − +
= − + −
= − +
= −




(23)

44
where , , ,a b c r are positive, constant parameters of the system.
The response system is described by the controlled hyperchaotic Yujun system as
1 2 1 2 3 1
2 1 2 4 1 3 2
3 3 1 2 3
4 4 1 3 4
( )y a y y y y u
y cy y y y y u
y by y y u
y ry y y u
= − + +
= − + − +
= − + +
= − +




(24)
where 1 2 3 4, , ,u u u u are the sliding mode controllers to be designed using the systematic procedure
outlined in Section 2.
The hybrid synchronization error is given by the definition
1 1 1
2 2 2
3 3 3
4 4 4
e y x
e y x
e y x
e y x
= −
= +
= −
= +
(25)
A simple workout yields the dynamics of (25) as
1 2 1 2 1
2 1 2 4 1 1 3 1 3 2
2 2
3 3 2 2 3
4 1 1 4
( ) 2
4 4 8 10( )
2
e a e e ae u
e e ce e x y y x x u
e be y x u
e de dx u
= − − +
= + + + − + +
= − + − +
= − − +




(26)
We write the error dynamics (26) in a matrix form.
Thus, we get the system
( , )e Ae x y u= + + (27)
In Eq. (27), the associated matrix and vectors are
0 0
4 0 4
,
0 0 0
0 0 0
a a
c
A
b
d
− 
 
 =
 −
 
− 
2
1 1 3 1 3
2 2
2 2
1
2
8 10( )
( , )
2
ax
x y y x x
x y
y x
dx

− 
 − + =
 −
 
− 
and
1
2
3
4
u
u
u
u
u
 
 
 =
 
 
 
(28)
Next, we carry out the sliding controller design for the hybrid synchronization of the hyperchaotic
systems considered in this paper.
For this paper, we first define u as
( , )u x y Bv= − + (29)

45
In (29), the matrix B is chosen such that ( , )A B is controllable.
A simple selection for B is
1
1
1
1
B
 
 
 =
 
 
 
(30)
We take the parameter values of the hyperchaotic Yujun system as
35, 3, 21a b c= = = and 2d = (31)
We also take the sliding mode variable as
[ ] 1 2 41 2 0 1 2s Ce e e e e= = − − = − − + (32)
The choice of C renders the system globally asymptotically stable in the sliding mode.
We take the sliding mode gains k and q as
6k = and 0.2q =
By making use of Eq. (15), we derive the sliding control ( )v t as
1 2 4( ) 9.5 44.5 0.1sgn( )v t e e e s= − − + (33)
Finally, for the hybrid synchronization of hyperchaotic Yujun systems, we get the sliding control
law given by the equation
( , )u x y Bv= − + (34)
Theorem 2. The identical hyperchaotic Yujun systems (23) and (24) are asymptotically hybrid
synchronized for all initial conditions by implementing the sliding mode controller u defined by
(34).
3.2 Numerical Results
The initial values of the master system (23) are taken as
1 2 3 4(0) 20, (0) 6, (0) 15, (0) 26x xx x= = − = =
and the initial values of the slave system (24) are taken as
1 2 3 4(0) 4, (0) 26, (0) 11, (0) 28y yy y= − = = − =
Figure 2 depicts the hybrid synchronization of the identical hyperchaotic Yujun systems.

46
Figure 3 depicts the time history of the synchronization error states 1 2 3 4( ), ( ), ( ), ( )e t e t e t e t .
Figure 2. Hybrid Synchronization of Identical Hyperchaotic Yujun Systems
Figure 3. Time History of Error States 1 2 3 4( ), ( ), ( ), ( )e t e t e t e t

47
4. CONCLUSIONS
This paper investigated the hybrid synchronization problem for the hyperchaotic systems using
sliding mode control (SMC) and derived some general results. Lyapunov stability theory was the
methodology used for proving these results. Using this general result for hybrid synchronization,
we derived a new sliding controller for achieving hybrid synchronization of the identical
hyperchaotic Yujun systems (2010). MATLAB simulation results were provided to illustrate the
results derived in this paper.
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48
AUTHOR
Dr. V. Sundarapandian graduated with D.Sc. degree in Electrical and Systems
Engineering from Washington University, St. Louis, Missouri, USA in May 1996. He is
working as Dean and Professor of the Research and Development Centre at Vel Tech
University, Chennai, Tamil Nadu, India. Dr. Sundarapandian has published over 320
research articles in refereed international journals. He has also published 2 books with
PHI, India and 1 book on Differential Equations with McGraw-Hill Education. He has
published over 200 articles in National and International Conferences. He is the India
Chair of AIRCC. He is the Editor-in-Chief of the five control journals – IJICS,
IJCTCM, IJITCA, IJCCMS and IJITMC - in AIRCC. His research interests are Control Systems, Chaos
Theory, Intelligent Computing, Operations Research, Optimal Control, Scientific Modelling and Numerical
Computing. He has delivered several Key Note Lectures on Control Systems, Chaos Theory and Scientific
Computing. He has conducted many Workshops on Mathematical Modelling, Computational Science,
Fuzzy Logic, Optimization, Operations Research, MATLAB and SCILAB.

ANALYSIS AND SLIDING CONTROLLER DESIGN FOR HYBRID SYNCHRONIZATION OF HYPERCHAOTIC YUJUN SYSTEMS

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