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Research On Robust Fault Tolerant Control For Nonlinear Systems Based On Fuzzy Model

Posted on:2009-10-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Y YinFull Text:PDF
GTID:1118360308478825Subject:Control theory and control engineering
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The reliability of control systems is the key to operate normally for practical systems. There are inevitable faults in actuators, sensors and other components which are parts of running control systems. It is very important signification to ensure the reliability and the security of control systems. The appearance of the fault tolerant control technology provides a new method to improve the reliability of control systems. Nowadays, the fault tolerant control for control systems as a frontier topic of control field has attracted more and more attention. The problems of robust tolerance are studied for a class of nonlinear systems with time delays or parameter uncertainties in this dissertation. The fuzzy models are proposed to describe the nonlinear systems with actuator failures. The sufficient condition has been obtained by using Lyapunov stability theory and linear matrix inequality (LMI) method for the existence of the fuzzy controller and ensures the robust stability of the system. The results of simulation demonstrate the effectiveness and the feasibility of the presented approaches.This work consists of following major parts:1. The problems of H∞robust fault tolerant control are discussed for a class of nonlinear systems with time delays. The systems described by T-S fuzzy models are proposed, according to continuous nonlinear systems and discrete nonlinear systems, which have state time delay and input time delay. The sufficient conditions for existence of desired fuzzy state feedback controller are obtained, which are independent on time delays. Based on Lyapunov stability theory and LMI method, an actuator failure matrix is introduced in the case of actuator fault in the system. The H∞performance index is satisfied by the conditions and the robust stability of the closed loop systems is assured.2. The problems of H∞robust fault tolerant control are discussed for a class of nonlinear systems with uncertainties and time delays.1) The problems of H∞robust fault tolerant control are discussed for a class of nonlinear systems with uncertainties, state time delays, and input time delays. The T-S fuzzy models are proposed to depict the continuous nonlinear systems with uncertainties and time delays, and the admissible parameter uncertainties are unknown and norm bounded. The state feedback controller is designed, and the sufficient conditions for the existence of desired fuzzy state feedback controller are obtained, which are independent on time delays. Based on Lyapunov stability theory and LMI method in the case of actuator fault in the system, the conditions assures the systems robust stability.2) The problems of H∞robust fault tolerant control are discussed for a class of nonlinear systems with uncertainties and state time delays. In order to obtain delay-dependent results, we use the Leibniz-Newton formula in the derivative of the Lyapunov function. The relationship among the terms of the nonlinear system and the relationship among the terms in the Leibniz-Newton formula are expressed by introducing some free weighting matrices. This treatment avoids difficulties and blindness in the handing of the Lyapunov function, and less conservative results are obtained. Sufficient conditions for the existence of desired fuzzy state feedback controller are obtained for the nonlinear system against actuator failures and external disturbance, the conditions are dependent on time delays and satisfies the H∞performance index of systems.3. The problems of H∞robust fault tolerant control are studied for a class of nonlinear systems with uncertainties and time-varying delays. The T-S fuzzy models are proposed to describe the nonlinear system and the admissible parameter uncertainties of state input and control input are unknown and norm bounded. Firstly, the memory fuzzy state feedback controller is adopted. The sufficient conditions for the existence of desired fuzzy state feedback controller are obtained and dependent on time delays, based on Lyapunov stability theory and LMI method in the case of actuator fault in the system. Secondly, the memoryless fuzzy state feedback controller is adopted. Different Lyapunov function is adopted, by using LMI technology, sufficient conditions for the existence of desired fuzzy state feedback controller are obtained and are dependent on time delays. The different controllers assure robust stability of the system, moreover, the H∞performance index is satisfied.4. Firstly, the problems of H∞, robust fault tolerant control are studied for a class of nonlinear descriptor systems with uncertainties and time delays. The descriptor T-S fuzzy models are proposed, and the admissible parameter uncertainties are unknown and norm bounded. The sufficient conditions for the existence of desired fuzzy state feedback controller are obtained and are independent on time delays. Based on Lyapunov stability theory and LMI method for the system against actuator failure, and the conditions assure the robust stability of the systems, and a prescribed H∞index for the nonlinear system with external disturbances. Secondly,.the problems of:H∞robust fault tolerant control are studied for a class of nonlinear descriptor systems with uncertainties and time delays, or time-varying delays respectively. Different Lyapunov function is adopted, some free weighting matrices are introduced in the derivative of the Lyapunov function. The sufficient conditions for the existence of desired fuzzy state feedback controller are obtained and dependent on time delays, which ensure the robust stability of the system.5. The problems of H∞robust fault tolerant control are discussed for nonlinear systems with uncertainties and time-varying delays. The fuzzy hyperbolic model is proposed to describe a class of continuous nonlinear systems with uncertainties and time-varying delays, and the admissible parameter uncertainties are unknown and normal bounded.A sufficient condition for the existence of desired fuzzy state feedback controller based on Lyapunov stability theory and LMI method for the nonlinear system against actuator failure is obtained, which assures robust stability and a prescribed H∞index for the nonlinear system with external disturbances.The conclusion is drawn for the whole dissertation, and the further research aspect is put forward.
Keywords/Search Tags:nonlinear system, T-S fuzzy model, fuzzy controller, uncertainty, time delay, stability, linear matrix inequality(LMI), fault tolerant control, robustness, fuzzy hyperbolic model
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