Circular Take-off and Landing for Motorized Kites in Airborne Wind Energy Systems

We address the problem of controlling a motorized kite of an Airborne Wind Energy System (AWES) during the take-off and landing maneuvers, using a circular path. Airborne Wind Energy (AWE) is the name given to concepts that convert wind energy into electricity, relying on autonomous kites or flying devices linked to the ground by one or more tethers. AWE systems offer several potential advantages over conventional wind turbines. They require less material than tower-based turbines, have the potential to be manufactured at a lower cost, can be quickly deployed and can harness stronger and steadier winds by flying at higher altitudes. One of the main challenges in AWES is the ability to operate safely, reliably, and autonomously for long periods of time in different weather and environmental conditions. For a complete flight cycle of the kite used on these systems and for it to function at its highest performance, it is mandatory to have an automatic take-off and landing of these systems. A solution is yet to be established, and various research teams and universities are still addressing this problem. To address this problem, we propose a circular take-off and landing (CTOL) approach, similar to [1], on which the kite has self-propulsion, and the tether is aligned with the wing during the kite acceleration. We use a modification of the model [2], [3] based on a mass–point model. We model a tethered kite with self-propulsion using Matlab/Simulink and develop a control scheme to confer the take-off and landing ability to an AWE system. The control inputs of the model are the throttle and the angle of attack of the kite. The kite starts in a rest position, having zero velocity. When performing the take-off procedure, the kite starts to accelerate, gaining velocity. Since it is connected to the ground station via a tether, the kite is forced to describe a circular path around the ground station. Using sliding mode control to uncover the relationship between the kite position and attitude and the inputs, namely the angle-of-attack and the throttle, we can increase its altitude, ensuring its safety. The same procedure is used for landing. The controllers resulting from our simulations are applied to a small-scale physical prototype.

REFERENCES:

[1] A. Cherubini, B. Szalai, R. Schmehl, and M. Fontana, “Automatic control-line flight for high altitude wind energy drones", Oct. 2017.

[2] G. B. Silva, L. T. Paiva, and F. A. Fontes, “A Path-following Guidance Method for Airborne Wind Energy Systems with Large Domain of Attraction” in 2019 American Control Conference (ACC), pp. 2771--2776, Jul. 2019.

[3] M. C. R. M. Fernandes, S. Vinha, L. T. Paiva, F. A. C. C. Fontes, "L0 and L1 Guidance and Path-Following Control for Airborne Wind Energy Systems", Energies, 15(1390), 2022.