Finite-time Adaptive Fault-tolerant Control For Uncertain Systems With Actuator Faults

As the application of the control system in modern production and life is becoming more and more important,its safety and reliability are highly valued.However,the faults caused by actuators,sensors and other components may degrade the system performance,and even lead to catastrophic accidents.Therefore,fault-tolerant control has attracted the attention of many researchers,and has obtained a series of research results in the past few decades.It is worth noting that most of the existing results guarantee the general stability of the system only,that is,the designed system performance may be reached when the time tends to infinite,and there is no time requirement for the performance of the system.However,it is required not only to be generally stable,but also to achieve the desired control effect within a finite time for a practical system,e.g.,the flight control system.As a result,the finite-time fault-tolerant control issue under actuator faults is researched in this paper,and the fault-tolerant control can be implemented directly without the fault detection and fault diagnosis module.First,considering a general deterministic system with actuator faults,in which the fault types include partial loss of effectiveness,outage and stuck,and the fault time,fault type and fault value are unknown.An adaptive fault-tolerant controller is designed based on adaptive control technology and finite-time control theory,and the adaptive update laws are designed to estimate the unknown parameters of the controller.The designed control algorithm can not only ensure the stability of the closed-loop system,but also guarantee that the state tracking error converges to a tunable neighborhood of the origin in a finite time.The proposed algorithm is applied to a class of high angle of attack lateral flight control system,and the simulation analysis shows that the stability and the finite-time tracking properties of the system can be guaranteed.Then,considering the fault-tolerant control problem of the uncertain system when there are multiple coupling uncertainties such as the uncertainty of the system matrix and input matrix,and the unknown actuator faults.A finite-time fault-tolerant controller is designed based on robust control idea.And the unknown parameters of the system and the upper bound of the model uncertainty are estimated by the designed adaptive update laws.Theoretical analysis shows that the proposed controller can guarantee the stability of the closed-loop system and the practical finite-time convergence of the state tracking error,and the convergence accuracy can be adjusted.The application results on a flight control system verify that the designed controller can achieve great robustness and finite-time tracking properties.It is impossible to increase or decrease the actuator output of a practical system without limitation,since it is usually limited by the physical structure.Consequently,a saturated fault-tolerant control scheme,which considers both the input saturation and multiple coupling uncertainties,is proposed for uncertain systems based on auxiliary system control method.A finite-time auxiliary system is designed to eliminate the effects of actuator saturation on the system.The unknown parameters of the system and auxiliary system are estimated by the designed adaptive update laws.Theoretical analysis shows that the stability of the closed-loop system and the finite-time convergence of the state tracking error can be guaranteed.The simulation results of a flight control system verify that the designed controller can guarantee the stability,anti-saturation performance and finite-time tracking properties of the closed-loop system.The research of this thesis provides control algorithm and theory for the fault-tolerant control of the system under actuator faults,and has great theoretical and practical application prospects.