Nonlinear Hierarchical Adaptive Control of a Quad Tilt-Wing UAV
Ahmet Eren Demirel
Mechatronics, MSc. Thesis, 2015
Prof. Dr. Mustafa Ünel (Thesis Advisor), Prof. Dr. Asif Şabanoviç, Assist. Prof. Dr. Hüseyin Üvet
Date & Time: August 5th, 2015 – 10.00 AM, Place: FENS 2019
Keywords : Quad-tilt wing UAV, Nonlinear Control, Feedback Linearization, Model Reference Adaptive Control
Unmanned aerial vehicles (UAVs) have become an indispensable part of many civilian and military applications. The popularity of these vehicles have led to a demand for novel mechanical configurations and controllers which are adaptable for the requirements of the desired tasks.
In this thesis, a nonlinear hierarchical adaptive controller is proposed for the control of a quad tilt-wing unmanned aerial vehicle (SUAVI: Sabanci University Unmanned Aerial Vehicle). SUAVI takes-off and lands vertically as a helicopter, performs a transition from vertical to horizontal flying mode by tilting its wings and flies like a fixed-wing airplane to optimize power efficiency for long duration flights. In order to compensate for the uncertainties such as moment of inertia changes during the transition from vertical to horizontal mode and aerodynamic disturbances, a two-level hierarchical adaptive control system is developed. In the outer loop of the hierarchical control system, a model reference adaptive controller with robustifying terms creates required forces to track the reference trajectory and in the inner loop a nonlinear adaptive controller tracks the desired attitude angles to achieve these forces. The proposed controller is applied to a high fidelity UAV model in the presence of uncertainties, wind disturbances and measurement noise. A structural failure is introduced which results in sudden actuator power drops, mass, inertia and center of gravity changes. Performance of the proposed controller is compared with the feedback linearized fixed controller used in earlier studies.