Stable Control Design Of Nonlinear Systems With Output Uncertainties

Considerable attention has been devoted to output feedback control of nonlinear systems in academic fields during the past decades.The intricate task is the reconstruction of some state variables which are not measurable.To overcome such difficulty,a series of effective methods were proposed based on the precise information on output functions,such as high-gain observers,K-filters,homogeneous observers and so on.This together with many constructive control schemes including backstepping,sliding mode control,adding a power integrator and time-varying feedback accelerated the development of output feedback stabilization for uncertain nonlinear systems.It is worthwhile pointing out that the technical limitation renders that the sensors failed to detect all state variables,so actual values of output function could deviate from its nominal values inevitably.Therefore,the investigation of the stabilization of uncertain nonlinear systems with time-varying output function opens up a new idea of control method research.The main contents of this paper are mainly carried out from the following two aspects:I.Global output feedback stabilization for a class of nonlinear cascade systems with time-varying output functionThis part focuses on the problem of global output feedback stabilization for a class of nonlinear cascade systems with time-varying output function.By using double-domination approach,an output feedback controller is developed to guarantee the global asymptotic stability of the closed-loop system.The novel control strategy successfully constructs a unified Lyapunov function,which is suitable for both upper-triangular and lower-triangular systems.And the effect of uncertainty caused by measurement error on the cascade system is solved for the first time.Finally,two numerical examples illustrate the effectiveness of a control method.II.Global finite-time output feedback stabilization for nonlinear system with timevarying output functionThis part studies the problem of global finite-time output feedback stabilization for a class of nonlinear systems with unknown time-varying output function.The continuous measurement error originating from inaccurate detection of system output disables the existing control schemes which are heavily dependent on the construction of an observer where the precise output must be used.A new finite-time convergent observer provided in this paper successfully gets rid of this obstacle according to avoid the use of the information on nonlinearities.The output feedback controller composed of multiple nested sign functions is developed by taking advantage of the homogeneous domination technique and the adding a power integrator method.Finally,the simulation example demonstrates the correctness of control strategy.