Showing papers by "Hassan K. Khalil published in 1994"

Adaptive output feedback control of nonlinear systems represented by input-output models

Abstract: We consider a single-input-single-output nonlinear system which can be represented globally by an explicit input-output model. The system is input-output linearizable by feedback and is required to satisfy a minimum phase condition. The nonlinearities are not required to satisfy any global growth condition. The model depends linearly on unknown parameters which belong to a known compact, convex set. We design a semiglobal adaptive output feedback controller which ensures that the output of the system tracks any given reference signal which is bounded and has bounded derivatives up to the (n+l)th order, where n is the order of the system. The reference signal and its derivatives are assumed to belong to a known compact set. It is also assumed to be sufficiently rich to satisfy a persistence of excitation condition. The design process is simple. First we assume that the output and its derivatives are available for feedback and design the adaptive controller as a state feedback controller in appropriate coordinates. Then we saturate the controller outside a domain of interest and use a high-gain observer to estimate the derivatives of the output. We prove, via asymptotic analysis, that when the speed of the high-gain observer is sufficiently high, the adaptive output feedback controller recovers the performance achieved under the state feedback one. >

Robust tracking for nonlinear systems represented by input-output models

Abstract: This paper deals with designing an output feedback control for a class of single-input, single-output nonlinear systems that are represented by input-output models. The authors augment a series of m integrators at the input side, where m is the highest derivative of the input, and redefine the output and its derivatives to obtain an (n+m)-dimensional state model, where n is the order of the system. The purpose of the design is to force the output to asymptotically track a time-varying reference signal, while rejecting a time-varying disturbance input. The authors assume that exogenous signals are generated by a linear exosystem. Also the authors assume that the nonlinearities of the system will introduce only a finite number of harmonics of the original modes. This will enable one to identify the internal model as a linear servo-compensator. After augmenting the original system with the servo-compensator, the authors present conditions that will characterize a state feedback stabilizing control. Then, using a high gain observer, the authors show that the asymptotic properties achieved under state feedback control can be recovered. >