Automatic crosswind flight of tethered wings for airborne wind energy: modeling, control design and experimental results

TL;DR

This paper presents a novel control approach for tethered wings in airborne wind energy that achieves figure-eight crosswind trajectories without needing wind speed measurements, validated through experiments.

Contribution

It introduces a wind speed-independent control method based on the wing's velocity angle, simplifying tuning and enhancing robustness for airborne wind energy systems.

Findings

Successful experimental validation on a small-scale prototype

Achieved stable figure-eight crosswind trajectories

Control system robust under varying wind conditions

Abstract

An approach to control tethered wings for airborne wind energy is proposed. A fixed length of the lines is considered, and the aim of the control system is to obtain figure-eight crosswind trajectories. The proposed technique is based on the notion of the wing's "velocity angle" and, in contrast with most existing approaches, it does not require a measurement of the wind speed or of the effective wind at the wing's location. Moreover, the proposed approach features few parameters, whose effects on the system's behavior are very intuitive, hence simplifying tuning procedures. A simplified model of the steering dynamics of the wing is derived from first-principle laws, compared with experimental data and used for the control design. The control algorithm is divided into a low-level loop for the velocity angle and a high-level guidance strategy to achieve the desired flight patterns. The robustness of the inner loop is verified analytically, and the overall control system is tested experimentally on a small-scale prototype, with varying wind conditions and using different wings.