Fault-tolerant Control Of Distributed Systems Based On Adaptive Technique

With the widespread popularity of control system in human’s various fields, the de-velopment of society is becoming more and more dependent on control system. The safety, reliability and effectiveness of system equipment has received great attention. The appearance and development of fault-tolerant technique has given a new way to improve safety and reliability of the system. The role of fault tolerant control system is charac-terized by that when actuators, sensors of the system and even system itself occur faults, the system operates in safety and maintains satisfied performance. In recent years, along with complex network of distributed control systems spring up in industry, actuators and sensors distribute in space largely. Coupled with the role of the network become increas-ingly prominent, the network security has been of great concern. More attention and requirements have been received for fault tolerant control.In the development of fault tolerant control during the past thirty years, based on robust control technique, passive fault tolerant control method designs a fixed controller gain for presumed faults, so that the feedback system is non-sensitive to the fault and opti-mizes the performance of each fault modes. On the other hand, active fault tolerant control method compensates for the effects of faults by adjusting controller on line to make sys-tem stable and to maintain satisfactory performances. Differing from FDI method which needs the diagnose mechanism to provide accurate fault signals, the adaptive method does not require the adaptive mechanism to provide accurate estimation signals. Thus it will not lead to failure of fault tolerance by misdiagnosis. Based on the adaptive fault tol-erant method, the existing papers mainly consider the problem of parameterized stuck faults compensation. Through the rational design of adaptive controller compensate for unparameterized stuck fault problem, disturbance rejection problems and optimizing per-formance problems of the system under the different models have not been given full consideration.On the other hand, this thesis considers fault tolerant control problem of distributed control systems with lossy interconnection. In complex large scale systems, each sub- system transmits signals through interconnected links or networks, and the transmitted signals determine the stability of systems, convergence and coordination of features, such as whether synchronization can be reached or not. However, in previous studies of dis-tributed systems, few results have considered lossy and perturbed interconnection. More-over, distributed system is composed by many actuators and sensors, and the probability of elements fault may greatly increase. Therefore, the study of fault tolerant of distributed systems is significant.Based on summarizing the existing results, this thesis studies the fault tolerant prob-lem of linear time-invariant system and distributed systems, respectively. On one hand, the thesis considers actuator faults of loss effectiveness and unparameterized time-varying stuck fault, and uses of an adaptive method adjustment controller on line to compensate fault effect, meanwhile to make the system capable of disturbance rejection. Further, com-bining LMI method with adaptive method, the system not only can compensate for fault effect but also can optimize system performance. Mode-dependent Lyapunov method has been utilized to reduce conservatism of design, and parts of theory results have been ap-plied in F-16 and F-18 aircraft models and rocket fairing structural-acoustic model. On the other hand, we design an adaptive distributed controller to guarantee the distributed system to asymptotically track reference signals in the cases of lossy interconnection and actuator faults. Moreover, adaptive designs can also guarantee synchronization of com-plex network with network deterioration.The main contributions are as follows:Chapters 1-2 first summarize and analyze the development and main research meth-ods in saturation problem. Preliminaries about the considered problem are also given.Chapter 3 studies the problem of robust fault tolerant control with actuators loss effectiveness and unparameterized stuck faults. The first part considers an indirect adap-tive method to design fault tolerant controller. Adaptive laws are given to estimate the constant fault factors, upper and lower bounds of stuck faults and external disturbances, respectively, then the adaptive signal is utilized to construct an adaptive controller to com-pensate the effects of actuator faults and disturbances. The second part considers a direct adaptive method to design fault tolerant controller. Adaptive laws are proposed to esti-mate controller gains and an adaptive gain function is designed to construct an adaptive controller guaranteeing the system asymptotically stable. Simulation examples are given to further illustrate the efficiency of the proposed two methods.Based on Chapter 3. Chapter 4 presents state feedback and output feedback fault tol- erant controller design methods with performance optimization. The designed controller is composed by an H∞controller gain and an adaptive control gain function. Utiliz-ing LMI theory, this section proposes a mode-dependent Lyapunov function approach to divide the fault and system matrices, and make each fault mode have corresponding Lyapunov function. The method reduces the conservatism comparing with using same Lyapunov function over all fault modes. Meanwhile, designing adaptive control gain function completely compensates for actuator faults and disturbances and gets adaptive fault tolerant controller with performance optimization. The first part of this chapter stud-ies the state feedback case, and applies the controller to flight control system for tracking control problem. The second part studies the output feedback case, and obtains e-stable results with application of an aircraft model.Chapters 5 and 6 study the problems of stability and tracking control for distributed control systems with actuator faults and faulty and perturbed interconnections. Chapter 5 designs adaptive laws to adjust distributed controller parameters, and constructs an adap-tive distributed state feedback controller to solve the asymptotic tracking problem with lossy interconnection and disturbances. The first section of Chapter 6 proposes adap-tive laws to estimate fault factors and controller parameters and constant disturbances simultaneity. The distributed state feedback controller can be constructed to ensure that the system is asymptotically stable with actuators and interconnections loss effectiveness. The second section of Chapter 6 introduces a direct adaptive method for distributed delay systems to deal with model referee tracking problem in the presence of stuck faults and faulty and perturbed interconnections. Simulation results are given to verify the effective-ness of the proposed methods.Chapter 7 studies the synchronization problem of dynamical complex networks in the presence of imperfect network and network deterioration. The first section proposes adap-tive laws to estimate unknown network coupling strength and the upper and lower bounds of communication state errors and disturbances on-line. Then based on the information from adaptive schemes, a class of distributed robust adaptive controllers is constructed to guarantee that the networks achieve synchronization. In the second section, for a class of general uncertain dynamical complex network with network eterioration, adaptive laws are proposed to adjust unknown coupling factors, and also adaptive control gain func-tions are designed to construct fully equipped controllers and pinning controllers. The two controllers ensure the networks asymptotic synchronization and uniformly bounded, respectively. Simulation results are given to verify the effectiveness of proposed methods. Finally, the results of the dissertation are summarized and further research topics are pointed out.