Showing papers by "Hassan K. Khalil published in 2014"
TL;DR: This talk is a brief introduction to high-gain observers in nonlinear feedback control, with emphasis on the peaking phenomenon and the role of control saturation in dealing with it.
Abstract: In this document, we present the main ideas and results concerning high-gain observers and some of their applications in control. The introduction gives a brief history of the topic. Then, a motivating second-order example is used to illustrate the key features of high-gain observers and their use in feedback control. This is followed by a general presentation of high-gain-observer theory in a unified framework that accounts for modeling uncertainty, as well as measurement noise. The paper concludes by discussing the use of high-gain observers in the robust control of minimum-phase nonlinear systems.
663 citations
314 citations
TL;DR: This paper uses the common Lyapunov function theorem and an LMI condition to show that, under suitable conditions, the tracking error of the system goes to zero exponentially fast when a constant reference is considered, and proves that a servocompensator-based controller can stabilize a system with hysteresis without using hystereresis inversion.
24 citations
TL;DR: A Newton-Raphson algorithm is formulated to calculate the limit cycles, and it is proved that the amplitude and period of these limit cycles have linear relationships to system parameters.
Abstract: In this technical note, we study the properties of self-excited limit cycles in an integral-controlled system containing a play operator. A Newton-Raphson algorithm is formulated to calculate the limit cycles, and we prove that the amplitude and period of these limit cycles have linear relationships to system parameters. These results are confirmed in simulation, where we demonstrate the ability to predict the properties of the limit cycles.
17 citations
TL;DR: In this article, singular perturbation techniques are employed to derive an analytical approximation to the tracking error for a system consisting of fast linear dynamics preceded by a piecewise linear hysteresis nonlinearity, which is motivated by applications such as piezo-actuated nanopositioning.
Abstract: Analysis of closed-loop systems involving hysteresis is important to both the understanding of these systems and the synthesis of control schemes. However, such analysis is challenging due to the nonsmooth nature of hysteresis nonlinearities. In this paper, singular perturbation techniques are employed to derive an analytical approximation to the tracking error for a system consisting of fast linear dynamics preceded by a piecewise linear hysteresis nonlinearity, which is motivated by applications such as piezo-actuated nanopositioning. The control architecture considered combines hysteresis inversion and proportional-integral feedback, with and without a constant feedforward control. The analysis incorporates the effect of uncertainty in the hysteresis model, and offers insight into how the tracking performance depends on the system parameters and the references, thereby offering guidance in the controller design. Simulation and experimental results on a piezo-actuated nanopositioning system are presented to support the analysis. In particular, the control scheme incorporating the feedforward element consistently outperforms the classical PI controller in tracking a variety of references. [DOI: 10.1115/1.4026511]
6 citations