Finite-time Adaptive Fuzzy Tracking Control For Uncertain Nonlinear Systems

With the rapid development of science and technology and modern industry,the controlled objects and system structures are becoming increasingly complex,which often present serious nonlinearity,uncertainty and multivariable properties.Therefore,the discussion and research of the control problems for uncertain nonlinear systems not only have critical theoretical significance,but also have extensive practical application value.Based on the existing research results,this thesis investigates the finite-time adaptive fuzzy tracking control problems for several classes of uncertain nonlinear systems by using adaptive control,fuzzy logic systems,backstepping recursive design and finite-time Lyapunov control theory.The main contents of this thesis are summarized as follows:1.An adaptive finite-time fuzzy prescribed performance control scheme is constructed for a category of strict-feedback nonlinear systems in presence of input delay and external disturbances.The unknown nonlinear functions in the controlled systems are approached by the fuzzy logic systems,a fuzzy state observer is established to estimate the incompletely measurable state variables in the systems.For the input delay issue,the Pade approximation method is employed to eliminate the influences.Based on the finite-time Lyapunov control theory,a finite-time fuzzy controller is designed,and then the stability of the closed-loop systems is analyzed.The simulation examples are given to illustrate the effectiveness of the developed control strategy.2.The finite-time adaptive output feedback control issue is studied for a category of nonlinear systems in presence of quantized input signals and unknown time delays.In this part,a hysteresis quantizer is used to avoid chattering in the quantized signals,and a suitable Lyapunov-Krasovskii functional is constructed to overcome the effects of unknown state delays on nonlinear systems.In the design process of adaptive backstepping control,an observer-based finite-time fuzzy control scheme is established by introducing dynamic surface control technology,which eliminates the ‘explosion of complexity' problem in traditional backstepping control technology.According to the finite-time Lyapunov stability theory,it is proved that the problems of the finite-time stability of the proposed controlled systems and the convergence of the tracking error.The simulation results are provided to verify the feasibility of the control design scheme.3.For a category of nonstrict-feedback time-delay nonlinear systems in presence of full state constraints and input saturation,the finite-time adaptive fuzzy tracking control issue is investigated.An appropriate Lyapunov-Krasovskii functional is constructed to eliminate the influences of the unknown state delays in the systems.In order to overcome the problem of full state constraints in the systems,a novel tan-type barrier Lyapunov function is introduced.By combining backstepping technology with finite-time control theory,a finite-time adaptive fuzzy controller is designed.The controller can not only ensure that the tracking error converges to a small neighborhood of the origin in a finite time,but also ensure the boundedness of all signals in the closed-loop systems.The simulation examples are given to show the feasibility of the developed control method.4.For a category of nonstrict-feedback nonlinear systems in presence of unknown control directions,the adaptive finite-time event-triggered command filtered control problem is studied.In the control design process,the event-triggered mechanism is utilized to reduce the communication burden between the controller and the actuator.The finite-time command filter is applied to avoid the ‘explosion of complexity' caused by the backstepping method,and an error compensation system with fraction power is constructed to compensate the filtering errors between the command filter and the virtual control signals.By means of the command filtering technology and event-triggered mechanism,a finite-time adaptive output feedback event-triggered control scheme is developed,and the stability of the controlled systems in the sense of finite time is proved.Finally,a simulation example is included to verify the availability of the control design approach.