Research On The Sampled-data Control Of Switched Nonlinear Systems

With the rapid development of science and technology,the control systems are often nonlinear and have become more and more complex in modern engineering applications.Due to the influences of external operation environment or their own factors,many practical systems own switching characteristics.In other words,these systems can be described as switched nonlinear systems.Meanwhile,with the wide applications of digital computers in various control fields,the sampled-data control has become a research hotspot because of its advantages of cost saving and easy implementation.In recent years,fruitful results have been obtained in the study of sampled-data control of nonlinear systems.However,most of the existing results focus on non-switched systems,and there are few related results for swithced nonlinear systems.In addition,how to further reduce the usage of communication resources on the basis of sampled-data control method has become an urgent and challenging problem.Therefore,the common Lyapunov function,average dwell time,backstepping design,fuzzy adaptive control,decentralized control and event-triggered control methods are used to investigate the sampled-data control problem for several kinds of switched nonlinear systems in this paper.Some restrictions on the systems in the existing results are relaxed,and thus the designed schemes have a wider application range.The control problem of switched nonlinear systems with the asynchronous phenomenon between the active subsystem and the activated controller is dealt with.On the basis of fixed-period sampled-data control method,the eventtriggered control method is introduced to further reduce the waste of communication resources.The contents of this dissertation improve the sampled-data control theory of switched nonlinear systems and enrich the research results in this field.The main contents of this dissertation are as follows:(1)The fuzzy adaptive state feedback sampled-data control problem for a class of switched nonlinear systems under arbitrary switchings is considered.Fuzzy logic systems are introduced to deal with unknown nonlinear terms.A novel fuzzy adaptive law is constructed by only using the information of the system state at sampling instants.In order to ensure that all states of the closed-loop system are semi-globally uniformly ultimately bounded under arbitrary switchings,a suitable common Lyapunov function is chosen and a novel fuzzy adaptive state feedback sampled-data controller is constructed.Finally,a simulation example is given to verify the effectiveness of the proposed scheme.(2)The fuzzy adaptive output feedback event-triggered control problem under arbitrary switchings for a class of switched nonlinear systems is discussed.In the considered system,only the system output at sampling instants is utilized.A state observer and a novel adaptive law are constructed by using only the sampled system output.A new fuzzy adaptive output feedback event-triggered control strategy is developed to reduce the usage of communication resources;it includes a controller that only uses event-sampling information and an event-triggering mechanism that is only intermittently monitored at sampling instants.Different from some existing results,the proposed fuzzy adaptive output feedback event-triggered control strategy does not need some restrictions on nonlinear functions of the considered system.It is proven that all states of the closed-loop system are semi-globally uniformly ultimately bounded under arbitrary switchings by choosing an allowable sampling period.Finally,the effectiveness of the proposed scheme is verified by simulation results.(3)The state feedback sampled-data control under average dwell time constraints for a class of switched nonlinear systems is investigated.Firstly,a state feedback controller in which the switching signal is detected only at sampling instants is constructed by only using the sampled system state information.Then,the asynchronous phenomenon between the active subsystem and the activated controller caused by detecting the switching signal only at sampling instants is discussed.A relationship,which can guarantee that the closed-loop system is globally asymptotically stable,between the sampling period and the average dwell time is established.Finally,the simulation results verify the effectiveness of the scheme.(4)The output feedback sampled-data decentralized control problem for a class of switched nonlinear interconnected systems with average dwell time constraints is studied.By using the system outputs at sampled-data instants,a new mode-dependent state observer is designed to estimate the unmeasured states and an output feedback sampled-data decentralized controller is constructed.By deriving a relationship between the sampling period and the average dwell time,the asynchronous switching problem between the controller and the subsystem caused by only detecting the switching signal at sampling instants is dealt with.Through stability analysis,it is proven that the closed-loop system is globally asymptotically stable under average dwell time constraints.Finally,the simulation results show the effectiveness of the proposed scheme.(5)The output feecback sampled-data decentralized control problem for a class of switched stochastic nonlinear interconnected systems under average dwell time constraints is considered.A state observer which only detects the switching signal at sampling instants is constructed by only using the sampled system outputs.Then,an output feedback sampled-data decentralized controller is designed,and a relationship between the sampling period and the average dwell time is established.Through the stability analysis,it is proven that the closed-loop system can still be guaranteed to be globally asymptotically stable in mean square under average dwell time constraints even if there is the asynchronous phenomenon between the active subsystem and the activated controller caused by detecting the switching signal only at sampling instants.Finally,a simulation example shows the effectiveness of the scheme.(6)The output feedback event-triggered control problem for a class of switched nonlinear systems under average dwell time constraints is investigated.In the considered system,only the system output at sampling instants is used and the switching signal is only detected at sampling instants.To estimate the unmeasured system states,a mode-dependent state observer is constructed by utilizing sampled system output information.A new output feedback event-triggered control scheme,which includes an event-triggered output feedback controller only using states at event-triggering instants and a discrete-time event-triggering mechanism only intermittently monitored at sampling instants,is proposed to reduce the usage of communication resources.To ensure that the closed-loop system is globally asymptotically stable under average dwell time constraints even if asynchronous switchings caused by only detecting the switching signal at sampling instants occur between the controller and the subsystem,a relationship between the sampling period and the average dwell time is established.Finally,the effectiveness of the scheme is verified by simulation examples.