68 research outputs found
Control of Towing Kites for Seagoing Vessels
In this paper we present the basic features of the flight control of the
SkySails towing kite system. After introduction of coordinate definitions and
basic system dynamics we introduce a novel model used for controller design and
justify its main dynamics with results from system identification based on
numerous sea trials. We then present the controller design which we
successfully use for operational flights for several years. Finally we explain
the generation of dynamical flight patterns.Comment: 12 pages, 18 figures; submitted to IEEE Trans. on Control Systems
Technology; revision: Fig. 15 corrected, minor text change
On sensor fusion for airborne wind energy systems
A study on filtering aspects of airborne wind energy generators is presented.
This class of renewable energy systems aims to convert the aerodynamic forces
generated by tethered wings, flying in closed paths transverse to the wind
flow, into electricity. The accurate reconstruction of the wing's position,
velocity and heading is of fundamental importance for the automatic control of
these kinds of systems. The difficulty of the estimation problem arises from
the nonlinear dynamics, wide speed range, large accelerations and fast changes
of direction that the wing experiences during operation. It is shown that the
overall nonlinear system has a specific structure allowing its partitioning
into sub-systems, hence leading to a series of simpler filtering problems.
Different sensor setups are then considered, and the related sensor fusion
algorithms are presented. The results of experimental tests carried out with a
small-scale prototype and wings of different sizes are discussed. The designed
filtering algorithms rely purely on kinematic laws, hence they are independent
from features like wing area, aerodynamic efficiency, mass, etc. Therefore, the
presented results are representative also of systems with larger size and
different wing design, different number of tethers and/or rigid wings.Comment: This manuscript is a preprint of a paper accepted for publication on
the IEEE Transactions on Control Systems Technology and is subject to IEEE
Copyright. The copy of record is available at IEEEXplore library:
http://ieeexplore.ieee.org
Modeling, identification, estimation and adaptation for the control of power-generating kites
Large-scale kites, flying high-force crosswind trajectories, have been proposed for wind power generation. A two phase operational cycle generates net positive power using a ground-based motor/generator. In the traction phase the kite flies a high-force trajectory while reeling out the generator-connected tethers. A low-force retraction phase reels in the tethers and returns the kite to the start of the cycle. Highly variable conditions and significant uncertainty in the dynamics pose challenges to autonomous, well-controlled flight. The control task is divided into trajectory generation and tracking components and the most uncertain parameters in the model are identified online. The control structure uses these parameters in a robust framework resulting in an experimentally verified adaptive control scheme
Automatic crosswind flight of tethered wings for airborne wind energy: modeling, control design and experimental results
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.Comment: This manuscript is a preprint of a paper accepted for publication on
the IEEE Transactions on Control Systems Technology and is subject to IEEE
Copyright. The copy of record is available at IEEEXplore library:
http://ieeexplore.ieee.org
State Estimation for Kite Power Systems with Delayed Sensor Measurements
We present a novel estimation approach for airborne wind energy systems with ground-based control and energy generation. The estimator fuses measurements from an inertial measurement unit attached to a tethered wing and position measurements from a camera as well as line angle sensors in an unscented Kalman filter. We have developed a novel kinematic description for tethered wings to specifically address tether dynamics. The presented approach simultaneously estimates feedback variables for a flight controller as well as model parameters, such as a time-varying delay. We demonstrate the performance of the estimator for experimental flight data and compare it to a state-of-the-art estimator based on inertial measurements
Automatic Retraction and Full Cycle Operation for a Class of Airborne Wind Energy Generators
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.Comment: This manuscript is a preprint of a paper submitted for possible
publication on the IEEE Transactions on Control Systems Technology and is
subject to IEEE Copyright. If accepted, the copy of record will be available
at IEEEXplore library: http://ieeexplore.ieee.or
Autonomous take-off and landing of a tethered aircraft: a simulation study
The problem of autonomous launch and landing of a tethered rigid aircraft for
airborne wind energy generation is addressed. The system operates with
ground-based power conversion and pumping cycles, where the tether is
repeatedly reeled in and out of a winch installed on the ground and linked to
an electric motor/generator. In order to accelerate the aircraft to take-off
speed, the ground station is augmented with a linear motion system composed by
a slide translating on rails and controlled by a second motor. An onboard
propeller is used to sustain the forward velocity during the ascend of the
aircraft. During landing, a slight tension on the line is kept, while the
onboard control surfaces are used to align the aircraft with the rails and to
land again on them. A model-based, decentralized control approach is proposed,
capable to carry out a full cycle of launch, low-tension flight, and landing
again on the rails. The derived controller is tested via numerical simulations
with a realistic dynamical model of the system, in presence of different wind
speeds and turbulence, and its performance in terms of landing accuracy is
assessed. This study is part of a project aimed to experimentally verify the
launch and landing approach on a small-scale prototype.Comment: This is the longer version of a paper submitted to the 2016 American
Control Conference 2016, with more details on the simulation parameter
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