Showing papers by "Hassan K. Khalil published in 2008"

Performance Recovery of Feedback-Linearization-Based Designs

Abstract: We consider a tracking problem for a partially feedback linearizable nonlinear system with stable zero dynamics. The system is uncertain and only the output is measured. We use an extended high-gain observer of dimension n+1, where n is the relative degree. The observer estimates n derivatives of the tracking error, of which the first (n-1) derivatives are states of the plant in the normal form and the nth derivative estimates the perturbation due to model uncertainty and disturbance. The controller cancels the perturbation estimate and implements a feedback control law, designed for the nominal linear model that would have been obtained by feedback linearization had all the nonlinearities been known and the signals been available. We prove that the closed-loop system under the observer-based controller recovers the performance of the nominal linear model as the observer gain becomes sufficiently high. Moreover, we prove that the controller has an integral action property in that it ensures regulation of the tracking error to zero in the presence of constant nonvanishing perturbation.

High-gain observers in the presence of measurement noise: A nonlinear gain approach

Abstract: This paper studies a high-gain observer with a nonlinear gain. The nonlinearity is chosen to have a higher observer gain during the transient period and a lower gain afterwards, thus overcoming the tradeoff between fast state reconstruction and measurement noise attenuation. The observer is designed such that the behavior of the innovation process can be controlled separately from the other system states. This is accomplished by assigning one fast eigenvalue, with the remaining eigenvalues chosen relatively slow. Without this key step, the stability analysis for the proposed observer is unattainable. Recently, a switched observer approach has been investigated, but the nonlinear gain approach bypasses the complications associated with switching, with little to no appreciable degradation in performance. This paper presents a new model for the nonlinear observer, accompanied by a discussion focusing on the main ideas behind the proof.

A novel nonlinear output feedback control applied to the TORA benchmark system

Abstract: A novel nonlinear control scheme is applied to the TORA benchmark system. This approach incorporates a continuous implementation of sliding mode control and an extended high-gain observer, and is based on previous work on the stabilization of a non-minimum phase nonlinear system, under the assumption that its associated auxiliary system has a stabilizing controller. The rotor angle is the only measurement required by this controller, and the closed-loop system thus obtained has quite interesting properties. The performance characteristics of a full-order observer-based second order linear system were recovered through an iterative tuning procedure. The final design provides good transient performance and some robustness to perturbations in the masses of the cart and rotor.

Robust stabilization of non-minimum phase nonlinear systems using extended high gain observers

Abstract: A robust, stabilizing output feedback controller for systems in the normal form, which could potentially include systems with unstable zero dynamics, is presented. The control scheme adopted herein incorporates "smoothed" sliding mode control-chosen for its robustness properties as well as its ability to prescribe or constrain the motion of trajectories in the sliding phase-and an extended high gain observer to estimate one of the unknown functions. Stabilization in the case of an unknown control coefficient and uncertain constant parameters is shown.

Topology optimization applied to the design of a dual-mode filter including a dielectric resonator

Abstract: The finite element method is coupled with the topology gradient method for optimizing the shape of microwave components using a numerical model. The approach, which consists in minimizing a cost function with respect to the physical property of individual topological elements, is first described. Regarding given electrical specifications, the technique is applied for optimizing the distribution of dielectric material in 3D in order to improve the behavior of a classical dual-mode filter including a dielectric resonator.

Lyapunov redesign approach to output regulation of nonlinear systems using conditional servocompensators

Abstract: This paper studies the output regulation of nonlinear systems using conditional servocompensators. Previous work introduced the conditional servocompensator that acts as a traditional servocompensator in a neighborhood of the zero-error manifold, while acting as a stable system outside a boundary layer, leading to improvement in the transient response while achieving zero steady-state tracking error in the presence of time-varying exogenous signals. The conditional servocompensator tool was introduced for sliding-mode feedback controllers. This paper extends the technique to more general feedback controllers by using Lyapunov redesign and saturated high-gain feedback.

Output regulation of linear systems subject to input constraints

Abstract: This paper studies the output regulation problem for linear systems subject to input constraints It presents a new controller that uses a conditional servocompensator Previous work introduced the conditional servocompensator, which acts as a traditional servocompensator only in a neighborhood of the zero-error manifold, while acting as a stable system outside a boundary layer, leading to improvement in the transient response while achieving zero steady-state regulation error Starting with a low-gain stabilizing state feedback controller, based on the solution of an algebraic Riccati equation, Lyapunov redesign is used to implement the state feedback control in a saturated high-gain feedback form that includes the conditional servocompensator The design is extended to output feedback via a full-order high-gain observer

Topology gradient optimization in 2‐D and 3‐D for the design of microwave components

Abstract: A numerical model defined by a finite element method coupled with a topology gradient method is used for optimizing the shape of microwave components with respect to electrical specifications. The approach, which consists in minimizing a cost function with respect to the physical property of individual topological elements, which define the shape of the component, is first described. Regarding the given electrical specifications, the technique is applied for optimizing, respectively, in 2D, the distribution of metal upon the surface of a planar component and, in 3D, the distribution of dielectric material within a waveguide component. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2739–2743, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23751

Advanced Design and Manufacturing of Microwave Components Based on Shape Optimization and Ceramic Stereolithography Process

Abstract: A design technique based on a shape optimization strategy (topology gradient algorithm) and a 3D ceramic stereolithography process are described in this paper Our goals are to propose innovative components in terms of electric performances and topologies, by using these two approaches together Several components have been designed, manufactured and tested with success An example is given for the design of microwave filters including dielectric resonators

Shape optimization design and ceramic stereo-lithography process dedicated to microwave component manufacturing

Abstract: In this paper, the topology gradient is applied in 3D for optimizing the shape of dual-mode dielectric resonators, and improving the electrical behavior of these classical filter components. Reference and optimal dielectric resonators are then fabricated by a 3D ceramic stereolithography process.