Research Article | Open Access

Yeong-Jeu Sun, "Nonlinear Observer Design of the Generalized Rössler Hyperchaotic Systems via DIL Methodology", *Mathematical Problems in Engineering*, vol. 2012, Article ID 764798, 9 pages, 2012. https://doi.org/10.1155/2012/764798

# Nonlinear Observer Design of the Generalized Rössler Hyperchaotic Systems via DIL Methodology

**Academic Editor:**Jun-Juh Yan

#### Abstract

The generalized Rössler hyperchaotic systems are presented, and the state observation problem of such systems is investigated. Based on the differential inequality with Lyapunov methodology (DIL methodology), a nonlinear observer design for the generalized Rössler hyperchaotic systems is developed to guarantee the global exponential stability of the resulting error system. Meanwhile, the guaranteed exponential decay rate can be accurately estimated. Finally, numerical simulations are provided to illustrate the feasibility and effectiveness of proposed approach.

#### 1. Introduction

In recent decades, several kinds of chaotic systems have been widely explored; see, for instance, [1–11] and the references therein. This is due to theoretical interests as well as to an efficient tool for chaos synchronization and chaos control design. As a rule, chaos in many systems is a source of the generation of oscillation and a source of instability. Chaotic systems frequently exist in various fields of application, such as system identification, master-slave chaotic systems, secure communication, and ecological systems.

Form practical considerations, it is either impossible or inappropriate to measure all the elements of the state vector. The state observer has come to take its pride of place in system identification, filter theory, and control design. As we know, the tasks of observer-based control systems (with or without chaos) can be divided into two categories: tracking (or synchronization) and observer-based stabilization (or regulation). The state observer can be skillfully applied in observer-based stabilization, synchronization of master-slave chaotic systems, and secure communication. For more detailed knowledge, one can refer to [1, 2, 7–9, 11–14]. However, the state observer design of dynamic systems with chaos is in general not as easy as that without chaos. Motivated by the above reasons, the observer design of chaotic systems is actually crucial and meaningful. On the other hand, a variety of methods have been proposed for the observer design of systems, such as Chebyshev neural network (CNN), sliding-mode approach, passivation of error dynamics, separation principle, and frequency domain analysis; see, for instance, [15–20] and the references therein.

In this paper, the nonlinear state reconstructor of the generalized Rössler hyperchaotic systems is investigated. Using the DIL methodology, a nonlinear observer for such systems is provided to guarantee the global exponential stability of the resulting error system. Furthermore, the guaranteed exponential decay rate can be correctly estimated. Finally, numerical simulations are given to verify the effectiveness of proposed approach.

#### 2. Problem Formulation and Main Result

In this paper, we consider the generalized Rössler hyperchaotic systems as follows: where is the state vector, is the system output, , , and are the system parameters with . For the existence and uniqueness of system (2.1), we assume that all the functions , are sufficiently smooth.

The following assumption is made on system (2.1) throughout this paper.(A1)There exists a constant such that

*Remark 2.1. *It is noted that the Rössler hyperchaotic system [21] is the special cases of system (2.1) with

The objective of this paper is to search a nonlinear observer for system (2.1) such that the global exponential stability of the resulting error systems can be guaranteed. Before presenting the main result, let us introduce a definition which will be used in the main theorem.

*Definition 2.2. *System (2.1) is exponentially state reconstructible if there exist an observer and positive numbers and such that
where expresses the reconstructed state of system (2.1). In this case, the positive number is called the exponential decay rate.

Now we present the main result for the state observer of system (2.1).

Theorem 2.3. *System (2.1) with (A1) is exponentially state reconstructible. Besides, a suitable nonlinear observer is given by
**
In this case, the guaranteed exponential decay rate is given by , where is the unique solution to the following Lyapunov equation:
*

*Proof. *From (2.1), (2.5) with
it can be readily obtained that
This implies that
with , in view of (A1):

Let
The time derivative of along the trajectories of dynamical error system, with (2.9), (2.10), and (2.6), is given by
Thus, one has
It follows that
Consequently, we conclude that
in view of (2.8), (2.10), and (2.13). This completes the proof.

#### 3. Numerical Simulations

Consider the generalized hyperchaotic system:

*Case 1 ( or, equivalently, the Rössler hyperchaotic system). *It can be verified that condition (A1) is satisfied with . By Theorem 2.3, we conclude that system (3.1) with and is exponentially state reconstructible by the nonlinear observer:
with the guaranteed exponential decay rate .

*Case 2 (). *It can be verified that condition (A1) is satisfied with . By Theorem 2.3, we conclude that system (3.1) with and is exponentially state reconstructible by the nonlinear observer:
with the guaranteed exponential decay rate .

*Case 3 (). *It can be verified that condition (A1) is satisfied with . By Theorem 2.3, we conclude that system (3.1) with and is exponentially state reconstructible by the nonlinear observer:
with the guaranteed exponential decay rate .

The time response of error states for system (3.1) with Case 1–Case 3 is depicted in Figures 1, 2, and 3, respectively. From the foregoing simulations results, it is seen that system (3.1) with Case 1–Case 3, regardless of chaotic system or nonchaotic system, is exponentially state reconstructible by the nonlinear observers (3.2)–(3.4), respectively.

#### 4. Conclusion

In this paper, the generalized Rössler hyperchaotic systems have been presented, and the state observation problem of such systems has been investigated. Based on the DIL methodology, a nonlinear state reconstructor of the generalized Rössler hyperchaotic systems has been developed to guarantee the global exponential stability of the resulting error system. Besides, the guaranteed exponential decay rate can be accurately estimated. However, the state observation design for more general uncertain hyperchaotic system still remains unanswered. This constitutes an interesting future research problem.

#### Nomenclature

: | The -dimensional real space |

: | The set of |

: | The modulus of a real number |

: | The Euclidean norm of the vector |

: | The induced Euclidean norm of the matrix |

: | The transpose of the matrix |

: | The set of all eigenvalues of the matrix |

: | The symmetric matrix is positive definite |

: | The maximum eigenvalue of the symmetric matrix with real eigenvalues |

: | The minimum eigenvalue of the symmetric matrix with real eigenvalues. |

#### Acknowledgments

The author thanks the National Science Council of Republic of China for supporting this work under Grant NSC-100-2221-E-214-015. The author also wishes to thank the anonymous reviewers for providing constructive suggestions.

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#### Copyright

Copyright © 2012 Yeong-Jeu Sun. 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.