Showing papers by "Hassan K. Khalil published in 2000"

Output feedback control of nonlinear systems using RBF neural networks

Abstract: An adaptive output feedback control scheme for the output tracking of a class of continuous-time nonlinear plants is presented. An RBF neural network is used to adaptively compensate for the plant nonlinearities. The network weights are adapted using a Lyapunov-based design. The method uses parameter projection, control saturation, and a high-gain observer to achieve semi-global uniform ultimate boundedness. The effectiveness of the proposed method is demonstrated through simulations. The simulations also show that by using adaptive control in conjunction with robust control, it is possible to tolerate larger approximation errors resulting from the use of lower order networks.

Universal integral controllers for minimum-phase nonlinear systems

Abstract: We consider a single-input-single-output (SISO) nonlinear system that has a well-defined normal form with asymptotically stable zero dynamics. Using only knowledge of the relative degree and the sign of the high-frequency gain, we design an output feedback integral controller that asymptotically regulates the output to a bounded time-varying reference signal with a constant limit. We give regional as well as semi-global results. We also show that, for relative degree one and two systems, the proposed integral controller reduces to the classical PI and PID controllers, respectively.

On the design of robust servomechanisms for minimum phase nonlinear systems

Abstract: We consider a single-input single-output nonlinear system which has a well defined normal form with asymptotically stable zero dynamics. We study the design of a robust output feedback controller, that incorporates a linear servo compensator, to achieve asymptotic tracking and disturbance rejection. We determine the least amount of precise information about the plant that is needed to design the controller. Such design will be robust to plant parameters and uncertainties which are not used in the design calculations. We also study the robustness of the design to errors in determining the linear servo compensator. Such errors could arise from approximating a general continuous nonlinear function by a polynomial one, or from errors in determining the frequencies of the exogenous signals. We give regional as well as semiglobal results.

Output feedback sampled-data control of nonlinear systems using high-gain observers

Abstract: This paper studies sampled-data control of nonlinear systems using high-gain observers. The observer is designed in continuous time, then discretized using three different discretization methods. Closed-loop analysis shows that the sampled data controller recovers the performance of the continuous time controller as the sampling frequency and the observer gain become sufficiently large.

Robust speed control of induction motors: application to a benchmark example

Abstract: A non-linear 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 and constant, it ensures asymptotic regulation. The controller is applied, via simulation, to a benchmark example. Copyright © 2000 John Wiley & Sons, Ltd.

Robust stabilization of large amplitude ship rolling in beam seas

Abstract: The dynamics and control of a strongly nonlinear 3-DOF model for ship motion are investigated. The model describes the roll, sway, and heave motions occurring in a vertical plane when the vessel is subjected to beam seas. The ship is installed with active antiroll tanks as a means of preventing large amplitude roll motions. A robust state feedback controller for the pumps is designed that can handle model uncertainties, which arise primarily from unknown hydrodynamic loads. The approach for the controller design is a combination of sliding mode control and composite control for singularly perturbed systems, with the help of the backstepping technique. It is shown that this design can effectively control roll motions of large amplitude, including capsize prevention. Numerical simulation results for an existing fishing vessel, the twice-capsized Patti-B, are used to verify the analysis. @S0022-0434~00!02701-5#