Adaptive Fault-tolerant Control For Uncertain Nonlinear Systems With Actuator Failures

Actuator failures seem inevitable especially in modern control systems,which may lead to catastrophic accidents.On the other hand,actuator nonlinearities widely exist in physical actuators,which often cause undesired system behavior.Furthermore,the system uncertainties also deteriorate the system performance or even instability.For several nonlinear systems,adaptive fault-tolerant controllers are proposed based on adaptive control theory,fuzzy control theory,backstepping method and robust control theory in the presence of actuator nonlinearities,actuator failures and uncertainties.The main contents of dissertation are as follows:(1)Consider a class of uncertain nonlinear systems,with unknown parameters and unknown actuator failures,a novel high-gain K-filter is firstly developed for state observation.Then an adaptive high-gain controller is proposed by using of backstepping method.The boundedness of the closed-loop signals and the tracking performance are guaranteed.The problem of unknown high-frequency gain is addressed.An adaptive high-gain K-filter is designed to estimate the unmeasured states.Then,combined Nussbaum technology with backstepping design,an adaptive high-gain controller is proposed.The boundedness of the closed-loop signals and the tracking performance are guaranteed.Simulation results show that the adaptive failure compensation scheme is effective.(2)For a class of uncertain nonlinear systems,with unknown actuator failures and unknown actuator hysteresis,which can be approximated by Bouc-wen model,an adaptive high-gain Kfilters and an adaptive state/output feedback controller are proposed.Three types of high-gain functions are constructed to counteract the effects of the hysteresis,bounded modeling errors and bounded disturbances.It is shown that the proposed controllers ensure bounded signals and asymptotic tracking,despite the presence of unknown actuator failures.Simulation results verify the desired failure compensation performance.(3)For a class of triangular nonlinear systems,with unknown actuator failures and unknown actuator dead-zone,a novel fuzzy K-filters is established to estimate the unmeasured states,then an adaptive fault tolerant control scheme is proposed.Several high-gain functions are developed to counteract the effects of the disturbances.The boundedness of the closed-loop signals are guaranteed while the tracking performance can be made sufficiently small.A simulation model is provided to show the effectiveness of the proposed scheme.(4)For a class of non-triangular nonlinear systems,with unknown actuator failures and unknown actuator hysteresis,which exhibit unknown backlash nonlinearities,a developed K-filters is constructed by fuzzy logic system to estimate the unmeasured states.Then combined fuzzy adaptive control with backstepping method,an adaptive output feedback controller is proposed.For different disturbances,high-gain functions are developed to counteract the effects.All of the closed-loop signals are bounded while the tracking error converges to a small neighborhood of the origin.Simulation results illustrate the effectiveness of the proposed scheme.