A Robust Adaptive H∞ Controller for Full Flight Envelope of a Convertible UAV

Abstract

A Tilt-Rotor Unmanned Aerial Vehicle (UAV) is an underactuated mechanical system with highly nonlinear and coupled dynamics, that is often subjected to parametric uncertainties, unmodeled dynamics, and external disturbances. To cope with such adversities, this work proposes a robust adaptive controller capable of handling the full flight envelope of the UAV which is composed of cruise and hover flight modes. Most importantly, this work addresses the transition between hover and cruise flight and vice versa. To do so, a multi- body nonlinear dynamic model of a Quad-tiltrotor Convertible Plane (CP) Vertical Take-Off and Landing (VTOL) UAV, here called QuadCP-VTOL, is obtained using the Lagrangian formalism which takes into account nonconservative forces and torques applied by the propellers, tilting mechanisms, canards, wings, and horizontal stabilizers. Thereafter, a Linear Parameter Varying (LPV) model that covers the full flight envelope of the aircraft is derived from the nonlinear model. Accordingly to the adaptive mixing technique, several robust H∞ state feedback controllers are designed based on a parallel distribution compensation (PDC) method alongside a pole clustering technique to ensure better closed-loop performance. Results of numerical experiments conducted on a high fidelity simulator in a Hardware in the Loop (HIL) framework are presented to corroborate the efficacy of the proposed control strategy.