Adaptive fault tolerant control for a class of uncertain fractional‐order systems based on disturbance observer

Abstract

In this paper, a class of fractional-order nonlinear systems are considered in the presence of actuator faults. A novel fault tolerant control scheme based on disturbance observer has been presented, where the actuator faults are considered as the system disturbance and can be approximated by the proposed disturbance observer. The developed fault tolerant control guarantees the convergence of the closed-loop system and the output tracking performance. Finally, a simulation example is presented to verify the effectiveness of the new method. K E Y W O R D Sadaptive control, disturbance observer, fault tolerant control, fractional-order system INTRODUCTIONSince actuator fault is inevitable in modern control systems, which may degrade system performance, or even lead to system instability, compensation of actuator faults has significant impact on some critical physical systems. Adaptive fault tolerant control (FTC) has been shown as a desirable tool to this problem and remarkable progress have been made in the area. 1-8 Guang-Hong Yang proposes an adaptive output feedback control to deal with unknown nonaffine nonlinear faults for a class of nonlinear systems. 1 Salman Ijaz studies an active fault tolerant control (FTC) scheme for aircraft with dissimilar redundant actuation system in Reference 2. In Reference 3, fault-tolerant tracking control problem for a class of strict-feedback nonlinear systems subjected to actuator faults and external disturbances is investigated. Due to the global approximation performance of fuzzy logic system and neural networks, the authors in References 4-9 successfully solved the problem by introducing adaptive fuzzy logic control or adaptive neural networks control. Over the past decades, fractional-order systems 10,11 have attracted considerable attention due to the ability of describing long memory and hereditary characteristic of complex phenomenon in some practical systems. It can describe some systems more accurately than the traditional integer order method and has been widely applied in fields in engineering and physics, such as system biology, physics, chemistry, automatic control, materials science, engineering, etc. More and more fractional order systems have been studied, especially in tracking control performance and stability analysis. 12-18 Y. Wei et al. propose a variety of methods for the stabilization of fractional order systems. 12,14,15 Sufficient and necessary conditions for stabilizing singular fractional order systems are given in Reference 16. For a class of continuous-time fractional positive systems, stabilization control is addressed based on disturbance observer in Reference 17. The Lyapunov stability theory is extended to fractional-order nonlinear systems in References 13 and 18 and, where the concept of Lyapunov stability is defined and Lyapunov design method is proposed. As we all know, actuator or sensor faults may also occur in fractional-order systems due to poor working conditions, mechanical fatigue, and other factors. Consequently, how to detect and ...

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