Research On Adaptive Fault-Tolerant Tracking Control Methods For A Class Of Nonlinear Systems

With the sustainable development of science and technology,the scale and complexity of practical engineering control systems are increasing,which causes that the control systems often suffer faults.However,any type of failures may lead to the performance degradation of the whole controlled systems and affect their stability,and even cause unexpected economic losses or casualties.Hence,it is particularly important to improve the reliability and safety of control systems.The emergence and development of fault-tolerant control provides an effective way to solve this security problem.Considering that many practical engineering systems are strongly nonlinear,it is more theoretical and practical to study the fault-tolerant control problem of this class of systems.Due to the complexity of the nonlinear system itself,the development of its control theory is not perfect The corresponding fault-tolerant control methods mainly focus on studying the stability of faulty systems.However,the performance optimization problem of fault-tolerant control systems has received little attention.At present,the research on fault-tolerant control of actuators and sensors still has great limitations,and further investigations are needed.This dissertation studies the problem of adaptive fault-tolerant control for a class of uncertain nonlinear systems with lower triangular structure.Its control objective is to guarantee the stable system operation and expected tracking task completion in the presence of actuator or sensor faults.On the basis of the previous work and adaptive nonlinear control theory and combining Lyapunov function design,fuzzy/neural network approximation theory and adaptive signal compensation,this dissertation provides a serious of adaptive fault-tolerant controller design methods in presence of different fault types,performance indexes and practical constraints.The corresponding stability is analyzed by novel Lyapunov function methods.The simulations are conducted for single-link robot,three-order power network model,the experiment platform of tension control of vertical looper,and so on,to show the effectiveness of the proposed approaches.The full text of this dissertation is divided into eight chapters,and the main contents of each chapter are given as follows.Chapters 1-2 systematically introduce and analyze the background and development of the FTC,its related control methods and hot and difficult issues to be solved.The preliminary knowledge and research methods related to this dissertation are also provided.Chapter 3 investigates the FTC problem for a class of uncertain nonlinear systems with actuator fault and backlash-like hysteresis,and proposes a new adaptive faulttolerant controller with guarantee performance.The command filtering and prescribed performance techniques are used to mitigate the effects of dynamic errors and sufficiently improve the transient and steady-state performance.The resulting controller can compensate for the effects of actuator fault and backlash-like hysteresis and guarantee that the tracking error of the closed-loop system converges to a preset accuracy.Finally,the simulation results on single-link robot model are used to illustrate the effectiveness of the proposed method.Chapter 4 discusses the problem of output-feedback adaptive FTC for nonlinear pure-feedback systems in the presence of actuator fault and immeasurable state.The actuator simultaneously suffers partial loss of effectiveness and bias fault.First,a Butterworth low-filtering technique is applied to address the non-affine nonlinear function.The input mismatching problem between original system and observer is overcome by constructing an adaptive state observer,where the output tracking error is utilized for adaptive mechanism design.On the basis of this,combining backstepping technique and prescribed performance theory,the adaptive output-feedback fault-tolerant controller is designed.Such a design successfully remove the strict restrictions that the exact knowledge of system parameters are assumed to be known or the control input is priori bounded.Finally,the simulation experiments are carried out on tension control of vertical looper,and the simulation results demonstrate the effectiveness of the proposed scheme.Chapter 5 is concerned with the adaptive event-triggered FTC for the interconnected networked control systems.Differing from the existing event-triggered results,the chapter focuses on reduce the networked communication resource as much as possible on the premise of transient performance guarantees.To this end,a double event-triggered mechanism associated with transient performance constraint is designed.Then,by extending the existing K filtering and prescribed performance techniques,the output-feedback adaptive FTC controller is developed by using the sampling measurement data.Finally,a non-smooth Lyapunov analysis method is given to show the stability and performance guarantee of the closed-loop system.The simulation results are given to sustain the theoretic results.In Chapter 6,the problem of output-feedback adaptive FTC is considered for uncertain nonlinear systems with partial loss of sensor effectiveness.To address the challenges incurred by the inaccurate measurement of faulty sensor,a state observer with an adaptive fault compensation mechanism is first designed.By exploiting a cubic-function-based Lyapunov function,a piecewise increasing adaptive law is skilly constructed to online estimate the loss factor of effectiveness.On the basis,the adaptive fault compensation controller is developed and the stability of the resulting closed-loop system can be ensured.Finally,numerical simulations are provided to illustrate the effectiveness of the scheme.On the basis of these results,Chapter 7 investigates the problem of adaptive FTC for output interconnected nonlinear large systems with simultaneous sensor and actuator faults.However,the adverse coupling effects that unknown sensor faults and output interconnections coexist bring new challenges.First,a decentralized fault-tolerant observer is constructed to simultaneously estimate unmeasured state and compensate the actuator faults.Then,an adaptive signal compensation mechanism is presented to mitigate the effects of sensor faults and output interconnections.It is shown that the tracking error of each subsystem converges to an arbitrary neigh-borhood of zero.An example of a large-scale power system is adopted to illustrate the effectiveness of the obtained scheme.Chapter 8 summarizes the results of the dissertation and points out the future research topics.