Flight control of tethered kites in autonomous pumping cycles for airborne wind energy

TL;DR

This paper presents a flight control system for tethered kites used in autonomous airborne wind energy harvesting, focusing on direction control, flight pattern, and winch strategies, validated through real-world prototype data.

Contribution

It introduces a comprehensive control architecture and optimization-based winch strategies for efficient energy harvesting in autonomous kite systems.

Findings

Successful demonstration of autonomous pumping cycle operation

Effective direction control towards target points

Optimized winch strategies improve energy generation

Abstract

Energy harvesting based on tethered kites benefits from exploiting higher wind speeds at higher altitudes. The setup considered in this paper is based on a pumping cycle. It generates energy by winching out at high tether forces, driving an electrical generator while flying crosswind. Then it winches in at a stationary neutral position, thus leaving a net amount of generated energy. The focus of this paper is put on the flight control design, which implements an accurate direction control towards target points and allows for a flight with an eight-down pattern. An extended overview on the control system approach, as well as details of each element of the flight controller, are presented. The control architecture is motivated by a simple, yet comprehensive model for the kite dynamics. In addition, winch strategies based on an optimization scheme are presented. In order to demonstrate the real world functionality of the presented algorithms, flight data from a fully automated pumping-cycle operation of a small-scale prototype are given. The setup is based on a 30m$^2$ kite linked to a ground-based 50kW electrical motor/generator by a single line.