Aircraft dynamics with input rate constraints: An adaptive flight control application

Abstract

Magnitude and rate limitations imposed on the input signal in control systems can be handled using antiwindup compensator design procedures with near-optimal system performance guarantees in case the system experiences saturation. A problem of particular interest in handling input saturation nonlinearities using anti-windup compensation is the robust control of uncertain systems. An adaptive control design method has been recently developed based on an anti-windup scheme to recover the linear performance of systems with unknown parameters subject to input magnitude constraints and has been verified on an aircraft model. In this paper an extended adaptive control design for systems with input rate constraints is investigated for flight control applications based on the longitudinal dynamics of a glider Unmanned Aerial Vehicle (UAV) subject to significant input rate saturation nonlinearities limiting the aircraft's achievable soaring performance. The control surface actuator is modeled as a first-order lag and a symmetric rate-limiting nonlinearity, and an absorption method is applied to augment both the aircraft dynamics and the unconstrained controller. The adaptive law is combined with the augmented control structure using the certainty equivalence principle. A set of simulation results are presented to evaluate the performance of the adaptive control design methodology through different flight scenarios. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.