Showing papers by "Hassan K. Khalil published in 2005"
TL;DR: The first is asymptotic regulation and the second confirms the transient performance improvement by showing that the output feedback continuous sliding-mode control with integral action can be tuned to recover the performance of a state feedback ideal sliding mode control without integral action.
141 citations
TL;DR: In this article, a robust continuous sliding mode controller for output regulation of a class of minimum-phase nonlinear systems is proposed, where the servocompensator is designed as a conditional one that provides servocensation only inside the boundary layer.
Abstract: SUMMARY We consider the design of a robust continuous sliding mode controller for the output regulation of a class of minimum-phase nonlinear systems. Previous work has shown how to do this by incorporating a linear servocompensator in the sliding mode design, but the transient performance is degraded when compared to ideal sliding mode control. Extending previous ideas from the design of ‘conditional integrators’ for the case of asymptotically constant references and disturbances, we design the servocompensator as a conditional one that provides servocompensation only inside the boundary layer; achieving asymptotic output regulation, but with improved transient performance. We give both regional as well as semi-global results for error convergence, and show that the controller can be tuned to recover the performance of an ideal sliding mode control. Copyright # 2005 John Wiley & Sons, Ltd.
61 citations
TL;DR: In this article, a framework for the development of a fault detection and classification algorithm based on the coefficients calculated from the discrete wavelet transform and using clustering is described, and results from testing are presented, verifying the analysis.
58 citations
08 Jun 2005
TL;DR: In this paper, a logic-based switching design strategy was proposed to reduce the control efforts and improve robustness of a continuous high-gain-observer-based sliding mode control with respect to these nonideal operational conditions.
Abstract: We consider dynamic output feedback practical stabilization of uniformly observable nonlinear systems, based on high-gain observers with saturation. We assume that uncertain parameters and initial conditions belong to known but comparably large compact sets. In this situation, designs based on traditional robust or adaptive techniques, if applicable, would lead to high controller, observer, and adaptation gains. High gains may excite unmodeled dynamics and significantly amplify measurement noise. Moreover, they could be impossible or too costly to implement. In order to reduce the control efforts and improve robustness of a continuous high-gain-observer-based sliding mode control with respect to these nonideal operational conditions, we have recently proposed a new logic-based switching design strategy. In this paper, we generalize our technique and apply it to a wider class of nonlinear systems and more general Lyapunov-function-based state and output feedback designs. It is important to notice, in particular, that we require neither the sign of the high-frequency gain to be known nor the system to he minimum-phase. The key idea is to split the set of parameters into smaller subsets, design a controller for each of them, and switch the controller if the derivative of the Lyapunov function does not satisfy a certain inequality, after a dwell-time period. We do not order the candidate controllers in advance, as in our earlier work. Instead, we use estimates of the derivatives of the states, provided by an extended order high-gain observer, to calculate instantaneous performance indices. When the controller is falsified, we switch to a new controller that corresponds to the smallest index among the controllers that have not been falsified yet. This modification is important when the number of candidate controllers is high and pre-routed search may lead to an unacceptable transient performance.
40 citations
TL;DR: In this article, a conditional integrator is used to provide integral action inside a boundary layer while acting as stable systems outside, leading to improvement in transient response while achieving asymptotic regulation in the presence of unknown constant disturbances or parameter uncertainties.
Abstract: This paper studies the regulation of nonlinear systems using conditional integrators. Previous work introduced the tool of conditional integrators that provide integral action inside a boundary layer while acting as stable systems outside, leading to improvement in transient response while achieving asymptotic regulation in the presence of unknown constant disturbances or parameter uncertainties. The approach, however, is restricted to a sliding mode control framework. This paper extends this tool to a fairly general class of state feedback control laws, with the stipulation that we know a Lyapunov function for the closed-loop system. Asymptotic regulation with improvement in transient response is done by using the Lyapunov redesign technique to implement the state feedback control as a saturated high-gain feedback and introducing a conditional integrator to provide integral action inside a boundary layer. Improvement in the transient response using conditional integrators is demonstrated with an experimental application to the pendubot. Copyright © 2005 John Wiley & Sons, Ltd.
38 citations
TL;DR: This work considers a single-input–single-output minimum-phase nonlinear system with large parametric uncertainty and proposes a new approach based on partitioning the set of uncertain parameters into smaller subsets, designed for each subset.
35 citations
TL;DR: It is shown that a nonlinear output feedback stabilizing controller, which combines a globally bounded state feedback controller with a high-gain observer, is robust with respect to unmodeled fast actuator and sensor dynamics.
32 citations
21 Sep 2005-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, an adaptive feed-forward cancellation (AFC) control method is applied to damp sinusoidal disturbances due to microphonics in superconducting radio frequency (SRF) cavities.
Abstract: A control method, known as adaptive feedforward cancellation (AFC), is applied to damp sinusoidal disturbances due to microphonics in superconducting radio frequency (SRF) cavities. AFC provides a method for damping internal and external sinusoidal disturbances with known frequencies. It is preferred over other schemes because it uses rudimentary information about the frequency response at the disturbance frequencies, without the necessity for an analytic model (transfer function) of the system. It estimates the magnitude and phase of the sinusoidal disturbance inputs and generates a control signal to cancel their effect. AFC, along with a frequency estimation process, is shown to be very successful in the cancellation of sinusoidal signals from different sources. The results of this research may significantly reduce the power requirements and increase the stability for lightly loaded continuous-wave SRF systems.
24 citations
08 Jun 2005
TL;DR: This work studies the application of the "conditional integrator" technique to position control of a permanent magnet stepper motor, that results in better transient performance over conventional integral control in minimum-phase nonlinear systems.
Abstract: We study the application of the "conditional integrator" technique to position control of a permanent magnet stepper motor. This is a recent approach to the output regulation of minimum-phase nonlinear systems, that results in better transient performance over conventional integral control. Global regulation results are provided for state-feedback control and semi-global results under output-feedback. Simulation results show that good tracking performance is achieved, in spite of partial knowledge of the machine parameters.
3 citations
12 Dec 2005
TL;DR: The closed-loop behavior of the ex-tended Kalman filter for a class of deterministic nonlinear systems that are transformable to the special normal form with linear internal dynamics was studied in this article.
Abstract: We study the closed-loop behavior of the ex-tended Kalman filter for a class of deterministic nonlinear systems that are transformable to the special normal form with linear internal dynamics. We argue that the closed-loop system is asymptotically stable and the estimation error exponentially converges to zero. We compare the performance of the extended Kalman filter to a high-gain observer through the use of numerical examples.
3 citations