Research On Several Control Problems Of Uncertain Nonlinear Systems

Nonlinearities,time-delay,time-varying powers and other uncertainties and constraints conditions are commonly encountered in real systems,and the existence of uncertainties and the violation of constraints often result in system performance deterioration and system insta-bility.Hence,the research of control or constrained control for uncertain nonlinear systems and time-delay systems has received extensive attention.In this paper,some control problems of uncertain nonlinear systems are studied.The main research contents include:1.For a class of nonlinear time-delay systems with unknown output function and input matching uncertainty,whose nonlinearities contain the unknown constant,polynomial-of-input and polynomial-of-output growth rates.By constructing a new extended state observer and skill-fully combining the dynamic gain method,backstepping method with Lyapunov-Krasovskii(L-K)functional,a delay-independent output feedback controller is designed to ensure the bound-edness of all the closed-loop signals,the convergence of original system states and correspond-ing observer states and the input matching uncertainty estimation.2.For a class of feedforward nonlinear time-delay systems with unknown output function,whose nonlinearities contain the unknown constant,input function and polynomial-of-output growth rates.By skillfully combining the dynamic gain method,backstepping method with Lyapunov-Krasovskii(L-K)functional,a delay-independent output feedback controller with a simple dynamic gain is designed to ensure the boundedness of all the closed-loop signals and the convergence of original system states and corresponding observer states.3.For a class of feedforward nonlinear time-delay systems with unknown output function and input matching uncertainty,whose nonlinearities contain the unknown constant,polynomial-of-input and polynomial-of-output growth rates.In the case of relaxing the polynomial-of-output growth rate,by constructing a new extended state observer and skillfully combining the dynamic gain method,backstepping method with Lyapunov-Krasovskii(L-K)functional,a delay-independent output feedback controller is designed to ensure the boundedness of all the closed-loop signals,the convergence of original system states and corresponding observer states and the input matching uncertainty estimation.4.For a class of nonlinear systems with unknown output function and a known time-varying power,based on the adding a power integrator method and under a new nonlinear reduced-order observer,the maximal open sector of unknown continuous output function is giv-en by using a new parametric function,thus an output feedback controller is designed to make the equilibrium point of the closed-loop system is globally uniformly asymptotically stable.5.For a class of nonlinear systems with unknown multiple time-varying powers and full-state constraints,by constructing a log-type barrier Lyapunov function(BLF)and introducing higher and lower powers in control design together with the adding a power integrator method and adaptive method,a state feedback controller is designed such that under appropriate fea-sibility conditions,all the closed-loop signals are bounded,original system states converge to zero and full-state constraints aren't violated.6.For a class of nonlinear systems with unknown multiple time-varying powers and full-state constraints,with the help of a nonlinear state-dependent transformation,by introduc-ing higher and lower powers in control design and combining the adding a power integrator method with the dynamic gain method,a constrained tracking control design is given with-out frequently-used feasibility conditions,thus ensure the boundedness of all the closed-loop signals,the convergence of the tracking error and the constraint of full-states.7.For a class of nonlinear time-delay systems with unknown multiple time-varying pow-ers,input and full-state constraints,whose nonlinearities don't impose any restrictive growth condition.By utilizing the auxiliary control signal and nonlinear state-dependent transforma-tion to counteract the effect of input saturation and cope with full-state constraints,respectively,and then introducing higher and lower powers,Lyapunov-Krasovskii(L-K)functional and the Nussbaum function in control design together with the adding a power integrator method and adaptive neural networks(NNs)method,a delay-independent constrained tracking control de-sign is given without feasibility conditions,thus ensure the validity of NNs approximation,the boundedness of all the closed-loop signals and the constraint of input and full-states.