Study On Several Classes Of Adaptive Control Problems For Switched Systems

As a special class of hybrid systems,switched systems are of great significance both in theory development and engineering applications.Thus,switched systems have attracted increasing attention.A lot of results about switched systems have been reported focusing on switched systems without uncertainties.However,uncertainties exist in almost all systems in practice.The interaction of discrete dynamics,continuous dynamics and uncertainties makes the behaviors of an uncertain switched system become very compli-cated.The existence of parametric uncertainties blocks direct applications of traditional control design and analysis methods.How to design and analyze switched systems with parametric uncertainties is a problem worthy of study.This dissertation studies several class of adaptive control problems for switched systems with parametric uncertainties including H_? control,transient performance,asynchronous switching,stabilization problems.The related switching signals,controllers and adaptive laws are designed.The main contributions of this dissertation are as follows:(1)The problem of H_? state tracking model reference adaptive control for switched systems is investigated.To improve the transient performance of switched systems,the closed-loop reference model is introduced to switched systems.Firstly,neither the measurability of the system state nor the solvability of the H_? state tracking model reference adaptive control for each individual subsystem is required.The H_? state tracking model reference adaptive control problem for switched systems is solved by designing adaptive controllers for subsystems and a switching law.Then,we apply the proposed model reference adaptive control approach to an electro-hydraulic system to verify the effectiveness of the method.(2)For switched systems,we propose a multiple model adaptive control scheme with two-layer switching to improve the transient performance.Firstly,a finite time parameter identification model is presented which greatly reduces the number of identification models.Secondly,a two-layer switching strategy is proposed:The inner layer switching mechanism is to improve the transient behavior.The outer layer switching mechanism is to ensure the stability of the switched systems.Then,the proposed adaptive control scheme is shown to guarantee that all the closed-loop system signals remain bounded and the state tracking error converges to asmall ball whose radius can be made arbitrarily small.(3)The problem of model reference adaptive control for switched LPV systems is studied.Firstly,a switched LPV controller with adaptive laws is designed.Then,the proposed LPV controller with adaptive laws guarantees that all the closed-loop system signals remain bounded,and the state tracking error converges to a small ball centered at the origin whose radius can be made arbitrarily small.Finally,a practical example about model reference adaptive control for a turbofan-engine is given to demonstrate the validity of the designed method.(4)Based on the average dwell time method,the problem of model reference adaptivc control for nonlincar switched systems is proposed.Asynchronous switching between subsystems and the corresponding adaptive controllers is also considered.Firstly,a non-linear switched reference model is given,which can generate more sophisticated and more desired performance for requirement compared with the linear reference model.Secondly,an average dwell time is found which guarantees the boundedness of the reference model and the stability of the error system simultaneously.(5)The global stabilization for a class of switched nonlinear systems with vanishing control gains is investigated.Firstly,a sufficient condition ensuring the global stabilization of such a class of switched nonlinear systems is developed,which is also transformed into an optimization problem.Secondly,a control gain-dependent switching law is designed and a bounded switched controller is constructed.Then,the result is applied to a class of strict-feedback form switched nonlinear systems with vanishing control gains.Finally,as an extension,we study the adaptive stabilization for the switched nonlinear systems with parametric uncertainties.The conclusions and perspectives are presented in the end of the thesis.