Automatic retraction phase of airborne wind energy systems

Abstract

Airborne wind energy systems are an emerging technology to harvest wind energy at higher altitude. Renewable energy is produced by exploiting the aerodynamic lift exerted by a wing tethered to the ground and controlled to fly crosswind paths. System realizations with either on-board or ground-based generation are possible. The focus of this paper is on ground-based generation systems where a two phase cycle is carried out. In the traction phase, power is produced by reeling-out the tether, which is coiled around drums connected to generators; in the retraction phase, the tether is reeled-in after the maximum length has been reached. A new flight controller for the retraction phase, which is straightforward to implement and tune, is proposed and a theoretical analysis and simulation results are presented.