Showing papers by "Hassan K. Khalil published in 1997"

A separation principle for the stabilization of a class of nonlinear systems

Abstract: It is shown that the performance of a globally bounded partial state feedback control of an input-output linearizable system can be recovered by a sufficiently fast high-gain observer. The performance recovery includes recovery of asymptotic stability of the origin, the region of attraction. and trajectories.

Adaptive output feedback control of robot manipulators using high-gain observer

Abstract: An adaptive controller using only joint position measurement is presented for the tracking control of an n-link robot manipulator with unknown load. High-gain observers are used to estimate joint velocities. We saturate the control inputs outside a domain of interest and use an adaptive law with a parameter projection feature. Simulation results on a two-link manipulator illustrate that the proposed controller recovers the performance under state feedback.

Adaptive output feedback regulation of a class of nonlinear systems: convergence and robustness

Abstract: In this paper we consider a minimum-phase, input-output linearizable system that is represented globally by an nth-order differential equation. The nonlinearities of the system depend linearly on unknown parameters which belong to a known convex set. We design a semiglobal adaptive output feedback controller to ensure boundedness of all state variables and regulation of the output to zero (an open-loop equilibrium condition). It is shown that the adaptive controller is robust with respect to bounded disturbances in the sense that the mean square regulation error is of the order of the magnitude of the disturbance. Moreover, if the disturbance vanishes when the input and output are identically zero and if its slope is sufficiently small, then the adaptive controller will ensure convergence of the regulation error.

Robust control for a nonlinear servomechanism problem

Abstract: This paper deals with the design of output feedback control to achieve asymptotic tracking and disturbance rejection for a class of nonlinear systems when the exogenous signals are generated by a known linear exosystem. The system under consideration is single-input single-output, input-output linearizable, minimum phase, and modelled by an input-output model of the form of an nth-order differential equation. We assume that, at steady state, the nonlinearities of the system can only introduce a finite number of harmonics of the original exosystem modes. This assumption enables us to identify a linear servo-compensator which is augmented with the original system. Moreover, we augment a series of m integrators at the input side, where m is the highest derivative of the input, and then represent the augmented system by a state model. The augmented system is stabilized via a separation approach in which a robust state feedback controller is designed first to ensure boundedness of all state variables and track...

A robust torque controller for induction motors without rotor position sensors: analysis and experimental results

Abstract: A robust controller, which tracks flux and torque commands is designed for an induction motor. It is based on a transformation to the estimate of the rotor flux. The speed of the rotor is estimated from the stator currents using a high-gain observer. The controller is robust with respect to variations of the rotor resistance. Analysis of the controller shows that the system is asymptotically stable in the motoring and braking regions and in the generating region for large enough torque reference. Simulations and experimental results show agreement with the analysis.

Robust speed control of induction motors

Abstract: A nonlinear robust output feedback control is designed for a sixth-order model of an induction motor. The control uses only measurement of the rotor position and stator currents. It contains two observers, a second-order observer to estimate the rotor flux from the stator current and a third-order high-gain observer to estimate the rotor speed and acceleration from its position. The control is robust to uncertainties in the rotor and stator resistances, and a bounded time-varying load torque. It guarantees that the speed tracking error can be made arbitrarily small by choice of certain design parameters. Moreover, when the speed reference and load torque are constant, it ensures asymptotic regulation. Experimental results agree well with the analysis.

Input-output models for a class of nonlinear systems

Abstract: We investigate the possibility of having an input-output model that has a specific structure for multivariable input-output linearizable systems.