Journal of Control Science and Engineering

Volume 2016 (2016), Article ID 9735264, 8 pages

http://dx.doi.org/10.1155/2016/9735264

## An Approach of Tracking Control for Chaotic Systems

^{1}College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qingdao 266590, China^{2}Department of Electromechanical Engineering, Binzhou University, Binzhou, Shandong 256600, China^{3}School of Electrical Engineering and Automation, Qilu University of Technology, Jinan, Shandong 250353, China

Received 15 October 2015; Accepted 31 March 2016

Academic Editor: Jie Chen

Copyright © 2016 Jin Xing and Fangfang Zhang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Combining the ergodicity of chaos and the Jacobian matrix, we design a general tracking controller for continuous and discrete chaotic systems. The control scheme has the ability to track a bounded reference signal. We prove its globally asymptotic stability and extend it to generalized projective synchronization. Numerical simulations verify the effectiveness of the proposed scheme.

#### 1. Introduction

Since Ott et al. firstly proposed the method of chaos control in 1990 [1], chaos control has attracted great attention in recent years and lots of successful methods have been reported [2–22], such as feedback control [7, 8], impulsive control [9, 10], backstepping method [11], adaptive control [12–15], adaptive fuzzy backstepping technique [16], adaptive sliding mode control [17, 18], neural network technique [19], and synchronization [20–22].

However, due to the complexity of chaotic systems, most approaches are designed for a special chaotic system, or they only realize the control of unstable fixed point and synchronization for identical systems [7–10, 12–15]. The literatures on the tracking control of reference signal [23–32] are relatively less.

In 1998, Lin et al. applied the idea of Chen’s method [23] to discrete chaotic systems [24], but the method needed calculating an error feedback matrix to assure that a certain matrix is negative semidefinite. When the dimension of these matrixes is large, the calculation becomes rather complex. Chen established the open-plus-closed-loop control law for discrete dynamical systems [25], but it required that the initial points were in the basin of entrainment. References [26–28] realized tracking control only for Henon chaotic system. References [29, 30] presented tracking control schemes for continuous chaotic systems and did not refer to the application to discrete systems. Zheng et al. gave a rapid synchronization algorithm [31], but it involved the calculation of high order derivative matrix. Rehan et al. discussed stabilization and tracking control using linear matrix inequalities for a class of continuous systems satisfying global Lipschitz condition [32].

In practical engineering, we need to eliminate the chaos or transform them into some useful signals. Therefore, tracking control, which transforms the chaos signal into desired bounded signal, is significant in practice. Moreover, generalized projective synchronization (GPS) can transform into the problem of tracking control.

Based on the above discussions, we present a general tracking control scheme based on the Jacobian matrix and ergodicity of chaos. It is simple and does not refer to high order derivative matrix or other requirements such as global Lipschitz condition. The rest of the paper is organized as follows. In Section 2, the tracking control schemes for continuous and discrete systems and their mathematical proofs are given, respectively. In Section 3, we have applied this method to three chaotic systems and make simulations. Finally, the conclusions are drawn in Section 4.

#### 2. Theoretical Analysis

##### 2.1. Tracking Control for Continuous Chaotic Systems

Consider the following -dimensional continuous chaotic system: where the state variable vector , is -dimensional continuously differentiable nonlinear vector function, and is the controller. It is chaotic with .

The control objective is to design a novel controller such that the vector tracks the reference signal which satisfies where is -dimensional continuously differentiable nonlinear vector function.

Set the range of chaotic system as and the range of reference signal as . As the range of chaotic system is certain, we choose the reference signal satisfying . It is easy to implement in practice.

Theorem 1. *For systems (1) and (2), if we set and add the controllerwhere are the Jacobian matrix of and at , respectively, is a constant feedback diagonal matrix, and is the switch-off controller, which is depicted aswhere denotes the Euclidean norm and is a constant, then for the initial values which make (1) chaotic, That is, system (1) tracks system (2) asymptotically.*

*Proof. *The Taylor series of at iswhere is a polynomial vector which contains quadratic term and finite higher order terms of and .

Similarly,where is a polynomial vector like and .

When , according to (1)–(4), we haveWe introduce the following nonnegative Lyapunov function: ThenSince and , are polynomial vector composed of quadratic term and finite higher order terms of , there always exists satisfying .

When , the controller does not work. As there exist and satisfying , we let . According to the ergodicity of chaos, there always exists a certain time satisfying in the set , and system (1) always comes into the domain of in a limited time; thus, it asymptotically tracks the reference signal with controller (3). The proof is completed.

*Remark 2. *The value of is related to according to (10). The larger the is, the quicker the convergence is. However, it is difficult to calculate specific value of . In practice, the value of can be increased from zero for an appropriate convergence speed.

##### 2.2. Tracking Control for Discrete Chaotic Systems

Consider -dimensional discrete chaotic system or data-sampling system: where the state variable , is -dimensional continuously differentiable nonlinear vector function, and is the controller. It is chaotic with .

The drive system or the reference signal is denoted as where is -dimensional continuously differentiable nonlinear vector function. Like continuous systems, we assume there exist and satisfying .

Lemma 3 (see [33]). *Assume that there exists a function such that*(i)*, ; ; is positive definite and continuous with respect to the second argument;*(ii)*the variation of the function along the system ,**is negative definite. That is, there exists function satisfying , , , such that , where , .*

Then the origin of the system is asymptotically stable.

Similar to continuous system, we have the following.

Theorem 4. *For systems (11) and (12), if we set and add the controllerwhere are the Jacobian matrix of and at , respectively, is a constant feedback diagonal matrix, and the switch-off controller is depicted aswhere is a constant less than 1, then for the initial values which make (11) chaotic we have That is, system (11) tracks system (12) asymptotically.*

*Proof. *The Taylor series of at iswhere is a polynomial vector which contains quadratic term and finite higher order terms of and .

Similarly,where is a polynomial vector like and .

If , according to (11)–(14), we haveWe introduce the following nonnegative Lyapunov function:ThenBecause , and . Assume ; there always exists satisfyingTherefore, under the condition thatIt means .

If , the controller does not work. As there exist and satisfying ; according to the ergodicity of chaos, system (11) always comes into the range of in a limited time; thus, it asymptotically tracks (12). The proof is completed.

*Remark 5. *From (21), we know is the simplest situation for discrete systems. It can be extended to for specific system, where is a positive constant, which will be illustrated in the following simulations.

*Remark 6. *The value of is related to according to (21)–(24).

*Remark 7. *Compared with the controllers in [23–32], the proposed scheme is simpler and more general. It is suitable for continuous and discrete chaotic systems.

*Remark 8. *The proposed scheme has the ability to track a bounded signal satisfying .

*Remark 9. *The method can be extended to GPS.

For response system (1) (or (11) for discrete system) and a drive system (2) (or (12)), if (or ), where is the reversible scaling factor diagonal matrix, it is said that systems (1) and (2) (or (11) and (12)) realize GPS. Set (or ); therefore, GPS becomes complete synchronization between and (or and ).

#### 3. Examples

*Example 1 (Lorenz system). *The Lorenz system is depicted aswhere The system is chaotic with , , , and . The fourth-order Runge-Kutta scheme is utilized to solve the differential equations with . The initial point of the system is (1, −2, −1).

The reference signal is (), and it also can be depicted asAccording to (3), we have The tracking error and the controller are shown in Figure 1. From the track error in Figure 1, we conclude that the Lorenz system quickly tracks the reference signal.

To display the robustness of the proposed method, we add a uniformly distributed random noise to . Figure 2 indicates that eventually tracks the reference signal and ultimately slightly fluctuates around it.