Event-triggered Fault Diagnosis And Fault-tolerant Control

With the advancement of network communication and computing information tech-nologies,networked control systems(NCSs)have gained rapid development in recent years.Different from traditional point-to-point control systems,the data transmission be-tween plant,sensor,controller,actuator and other components of NCSs is realized by a shared communication network,which makes it possible to achieve resource sharing and remote control.Due to the advantages including simple installation and maintain-ability,NCSs have gained considerable application in a wide range of areas of industrial production and social life.Meanwhile,as the control systems become more and more large-scale and complex,the fault of system components and subsystems could lead to a collapse of entire control system,which may cause serious casualties and huge econom-ic losses.Thus,fault diagnosis and fault-tolerant control technologies are necessary to enhance the safety and reliability of control system.This dissertation is concerned with the fault diagnosis and fault-tolerant control problems of NCSs.To dealt with the lim-ited communication capacity of NCSs,event-triggered mechanisms are adopted to save limited communication resources,based on which the passive fault-tolerant control,fault detection,fault estimation and active fault-tolerant control are addressed for NCSs with event-triggered schemes.The main research contents of this dissertation are as follows:Considering a class of uncertain systems with actuator faults,the passive fault-tolerant control is addressed for systems under event-triggered communication.Recall-ing the fact that periodic sampling could lead to a higher bandwidth occupation of net-work communication while continuous event-triggered scheme could result in Zeno phe-nomenon,this dissertation considers the hybrid event-triggered scheme switching be-tween periodic sampling and continuous event-triggered scheme.This transmission mech-anism can not only save communication resources,but also avoid Zeno phenomenon fun-damentally since the time intervals between two consecutive triggering instants are larger than h.With considering the hybrid event-triggered scheme and transmission delay,the closed-loop system is reconstructed as a delay system in a switching form.By using time-delay system analysis theory,criteria are provided to ensure the stability and pas-sivity of system,based on which the co-design method of fault-tolerant controller and event-triggered scheme is deduced.Considering the high conservatism of full-frequency controller design method,the problem of finite-frequency passive fault-tolerant control is addressed for system with event-triggered scheme in this dissertation.The control system is stable in the entire fre-quency range while has an H? performance index in the specific concerned frequency domain.To balance the usage of communication resources and system performance,the adaptive hybrid event-triggered mechanism is constructed where the network bandwidth occupation rate is introduced as an adaptive parameter.When the occupation rate is high,a tighter event-triggered condition is adopted to reduce sending measurements;otherwise,a looser event-triggered condition is used to improve system performance.Considering the adaptive hybrid event-triggered mechanism and time-varying communication delay,the criteria of stability and finite-frequency H? performance is provided for closed-loop sys-tem with actuator faults,based on which the fault-tolerant controller and event-triggered scheme is co-designed.Although its simple structure and easy implementation,passive fault-tolerant con-troller needs to foresee all possible system faults,which means it has limited tolerance to system faults.In order to further improve the safety and reliability of the control system,we address the problem of active fault-tolerant control for NCSs with event-triggered communication in the rest of this dissertation.Firstly,the problem of event-triggered fault detection is studied.Traditional event-triggered mechanisms test the event-triggered condition by measurement at the sampling instants,which could trigger unnecessary da-ta transmissions and increase the burden of communication network since the existence of noise and disturbance.For the purpose of suppressing the influence of noise and disturbance on event-triggered condition,we consider an integral-based event-triggered scheme,which examines the event-triggered condition by the integral mean value of mea-surement in a fixed time period.By using delay partitioning approach and discontinuous Lyapunov-Krasovskii function,the co-design criterion is proposed such that the residual error has a given H? performance.Traditional residual evaluation mechanism usually need to pre-select constant thresh-old for residual evaluation function based on experience.However,it's always difficult to choose such appropriate thresholds in practice,which could affect the fault detection per-formance.To deal with this problem,we address the zonotopic fault detection for NCSs with event-triggered mechanism based on set-membership estimation theory.Considering a class of discrete-time control systems with amplitude-bounded disturbance and noise,a dynamic event-triggered communication mechanism is employed to save communication resources.An event-triggered l1/h? fault detection observer design criterion is deduced,where l1 performance ensures the robustness of residual to disturbance and noise,and h?performance guarantees the sensitivity of residual to system fault.Then,by using zono-tope technique,the interval estimation of residual is provided in fault-free case,based on which a dynamic residual evaluation algorithm is proposed.Finally,the problem of event-triggered fault estimation and fault-tolerant control is investigated for NCSs.Taking event-triggered scheme and time-varying transmission delay into consideration,a fault estimation observer is constructed to estimate the system state and fault signal,based on which active fault-tolerant controller can be well designed.By establishing a multi-objective problem,an event-triggered fault estimation observer design criterion is proposed to guarantee the estimation precision.Based on the estimated system state and fault signal,a fault-tolerant controller is designed to compensate the system faults in real time,such that the stability and prescribed H? performance can be guaranteed when system actuator fails,which improve the safety and reliability of the control system.