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A Trajectory Controller for Kite Power Systems
with Wind Gust Handling Capabilities
Manuel C. R. M. Fernandes, Gonc¸alo B. Silva, Lu
´
ıs Tiago Paiva and Fernando A. C. C. Fontes
SYSTEC–ISR, Faculdade de Engenharia, Universidade do Porto,
Rua Dr. Roberto Frias, Porto, Portugal
Keywords:
Renewable Energy, Airborne Wind Energy, Kite Power Systems, Nonlinear Systems, Path-following Control,
Safe Mode Control.
Abstract:
In this paper, we address the generation of electrical power using Airborne Wind Energy Systems, comprising
a kite connected through a tether to a generator on the ground. We design a controller to steer the kite to
follow a pre-defined periodic path, which includes a production mode, a tether retrieval mode, and a safe
mode capable of handling wind gusts.
1 INTRODUCTION
Electrical energy is crucial to satisfy modern human
needs, while the amount of energy available is directly
associated with development. Currently, the majority
of electrical energy generated worldwide comes from
fossil and nuclear fuels, which are now facing increas-
ing societal concerns of environmental sustainability.
To address these problems, countries are enact-
ing energy policies to encourage the use of renew-
able energies. In this context, in the last decades
there has been a fast growth and development of re-
newable energy systems. Very recently, Portugal’s to-
tal renewable energy production in March 2018 ex-
ceeded the country’s electricity consumption for the
month. Among the renewable energy sources, wind
is an important large scale alternative. Wind energy
is nowadays mainly extracted on-shore at low heights
by wind turbines mounted on towers with a few dozen
meters (50-200 m) and, despite the significant num-
ber, still growing, of wind farms, most of the existing
wind energy remains unexploited since it is available
at high altitudes and off-shore.
One of the promising technologies to exploit the
stronger and more consistent high altitude and off-
shore winds is Airborne Wind Energy (AWE), namely
Kite Power Systems (Ahrens et al., 2013; Schmehl,
2018). These systems use a kite, with flexible or rigid
wing, that is connected to a generator through a ca-
ble (tether). Most of such systems are based on ex-
ploiting crosswind kite power described by Loyd in
1980 (Loyd, 1980). The huge power that can poten-
tial be harvested from AWE systems is supported by
the facts that wind speeds grow fast with height and
that the aerodynamic lift is proportional to the square
of the apparent wind velocity
~
F
lift
=
1
/2c
L
(α)Av
2
a
. (1)
Thus, the maximum power extraction is obtained
when the kite flies at high speeds in direction perpen-
dicular to the direction of the wind, which requires
this trajectory to be periodic.
In a kite power system with a fixed generator on
the ground, which is our case, electrical power is gen-
erated as the kite rises by the wind, which causes the
cable to be unrolled and subsequently the generator
to produce electricity (see Figure 1). Since the cable
length is finite, when we reach that limit the cable is
retrieved with a minimum energy expenditure and the
process is repeated.
To automate this process and guarantee a positive
net power output it is necessary to design a controller
taking into account variations in wind direction and
intensity, among other factors.
Using a 3D simulation model of the kite dynam-
ics, considering all the forces acting on it, we design
a controller to follow a desired path. Then we ad-
dress the problem of handling wind gusts. When wind
reaches a certain speed threshold, where tether force
might be excessive, we activate gust mode in order to
prevent damage to the kite or other components. We
do this by stopping the kite reel-out (or reel-in, in case
the gust occurs in recovery mode), and directing it up-
wards to an equilibrium inclination. We set the angle
Fernandes, M., Silva, G., Paiva, L. and Fontes, F.
A Trajectory Controller for Kite Power Systems with Wind Gust Handling Capabilities.
DOI: 10.5220/0006914205330540
In Proceedings of the 15th International Conference on Informatics in Control, Automation and Robotics (ICINCO 2018) - Volume 1, pages 533-540
ISBN: 978-989-758-321-6
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
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