Automatic Retraction and Full Cycle Operation for a Class of Airborne Wind Energy Generators

TL;DR

This paper presents control strategies for retraction phases in airborne wind energy systems, supported by theoretical, simulation, and experimental analyses demonstrating autonomous power cycle performance.

Contribution

It introduces two novel control strategies for retraction in airborne wind energy generators, validated through comprehensive simulations and experiments.

Findings

Effective control strategies for retraction phase demonstrated

Autonomous power generation cycles successfully implemented

Experimental results align with theoretical models

Abstract

Airborne wind energy systems aim to harvest the power of winds blowing at altitudes higher than what conventional wind turbines reach. They employ a tethered flying structure, usually a wing, and exploit the aerodynamic lift to produce electrical power. In the case of ground-based systems, where the traction force on the tether is used to drive a generator on the ground, a two phase power cycle is carried out: one phase to produce power, where the tether is reeled out under high traction force, and a second phase where the tether is recoiled under minimal load. The problem of controlling a tethered wing in this second phase, the retraction phase, is addressed here, by proposing two possible control strategies. Theoretical analyses, numerical simulations, and experimental results are presented to show the performance of the two approaches. Finally, the experimental results of complete autonomous power generation cycles are reported and compared with first-principle models.