Adaptive Fault Tolerant Control For Complex Nonlinear Systems

With the development of control system,its reliability and safety have received more and more attention.However,as the system structure becomes more and more complex and the scale of the system is becoming larger and larger,the actuators and sensors will inevitably fail,which will decline the system control performance,and even lead to the instability of the closed-loop system.Therefore,how to design effective fault-tolerant controllers for nonlinear system with actuator and sensor faults to ensure the stable operation of the system is of essential both theoretical and practical importance.Based on adaptive backstepping control method,fuzzy logic systems,fault-tolerant control method,stability theory of nonlinear and stochastic nonlinear systems,the fault-tolerant control problems of different types of complex nonlinear systems with sensor or actuator fault are studied in depth in this thesis.The main contents of this thesis are as follows:The fault-tolerant control problem for a class of strict-feedback nonlinear systems with external disturbances,unknown input dead time and actuator failure is investigated.Firstly,the fuzzy logic system is used to approximate the unknown nonlinear term in the system,and a new disturbance variable,which is unknown,is constructed based on the fuzzy approximation error and the external disturbance of the system.The disturbance observer is designed to estimate the unknown disturbance variable in the control design process.Secondly,the control input of the system is expressed as a nonlinear function of the unknown dead zone input,and the corresponding parameter adaptive law and adaptive fuzzy fault-tolerant control method are designed by backstepping method.The Lyapunov stability theory is utilized to analyze the stability of the closed-loop system,which is guaranteed to be stable and all the signals are semi global uniformly ultimately bounded.Then,we investigated the fault-tolerant control problem for a class of stochastic strict-feedback nonlinear systems with both quantized input and actuator faults is investigated.Firstly,fuzzy logic system is used to approximate unknown nonlinear functions,and a fuzzy state observer is designed to estimate the unmeasurable state.Secondly,by expressing the quantized input signal as a nonlinear function of the input signal,the corresponding parameter adaptive law and adaptive fuzzy fault-tolerant control method are designed based on It (?) calculus theory and adaptive backstepping method.Furthermore,the Lyapunov stability theory is utilized to analyze the stability of the closed-loop system,which is guaranteed to be stable in probability.The fault-tolerant control problem for a class of It (?) stochastic nonlinear system with unknown parameter,sensor faults and unknown control directions is investigated.Firstly,all the system state sensors are assumed to experience partial loss-of-effectiveness faults,and that all the system states effected by the unknown control directions.Secondly,the change of coordinates is given based on adaptive backstepping design technique,and exponential type Lyapunov function is designed to analyze the stability in probability of the closed-loop system.Finally,the adaptive fault-tolerant control strategy is proposed based Nussbaum type function to compensate the effect of sensor faults and unknown directions.The fault-tolerant control problem for single-input and single-output(SISO)stochastic strict-feedback nonlinear system and stochastic interconnected nonlinear system with both sensor and actuator faults are investigated.The control output feedback fault-tolerant problem for SISO system is first considered,and then it is extended to the case of interconnected case.The fuzzy logic system is used to approximate the unknown nonlinear function of the system and a fuzzy state observer is constructed to estimate the unmeasurable state and failure ratio constant.Then,based on the augmented estimation error system,a novel combined quadratic and cubic Lyapunov function is designed.and the corresponding parameter adaptive law and adaptive fuzzy fault-tolerant control method for both SISO and interconnected stochastic nonlinear systems are designed to ensure that the state variables of the closed-loop system are semi globally uniformly ultimately bounded in probability.The fault-tolerant control problem for a class of stochastic Markovian jump purefeedback nonlinear systems with time-varying delay and actuator faults is investigated.Firstly,the system fault model is expressed as a nonlinear fault model with dead zone characteristics,and the coordinate transformation with Markov variables is given.Secondly,based on the coordinate transformation,the parameter adaptive law and adaptive fault-tolerant control method are designed.The stability of the system is analyzed by using the stochastic system theory to ensure that the state variables of the closed-loop system are bounded in probability.Furthermore,the proposed control algorithm is applied to a class of practical active suspension control system to verify its effectiveness.