A hierarchical control strategy for the autonomous navigation of a VTOL

Abstract—This paper describes a control strategy to stabi-lize the position of a Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicle (UAV) in wind gusts. The proposed approach takes advantage of the cascade structure of the system to design a hierarchical controller. The idea is to separate the controller in a High Level Controller devoted to position control and a Low Level Controller devoted to stabilization and attitude control. Both controllers are designed by means of backstepping techniques that allow the stabilization of the vehicle’s position while on-line estimation of the unknown aerodynamic forces. The global stability of the connected system is proven, and simulations as well as experimental results are presented. I