the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A small-scale and autonomous testbed for three-line delta kites applied to airborne wind energy
Abstract. A mechanical control system and the guidance and control modules of a small-scale and autonomous testbed for three-line kites applied to airborne wind energy are presented. It extends the capabilities of a previous developed infrastructure by (i) changing the actuation system to add a third tether to control the kite pitch angle, (ii) adding running line tensiometers to measure the three tether tensions while allowing tether reel-in and reel-out, and on-board load cells to measure the bridle tensions, (iii) a real-time control system to operate the kite autonomously in figure-eight trajectories. A controller based on a hybrid guidance scheme for figure-eight flight paths, which combines attractor points for the straight segments and a continuous heading angle tracking for the turns, was implemented and validated in an experimental campaign. Two flights of the campaign were used to illustrate the performance of the controller and its capability to adjust the lateral amplitude, elevation and radius of the turns by varying a few parameters of the guidance module. The proposed control scheme was proven effective in achieving satisfactory and repeatable figure-eight paths. The experimental data collected during the autonomous flight was used to investigate the dynamics and control of the kite and the tethers. A correlation between the heading and roll angles of the kite was identified and modeled with a simple analytical law with empirical coefficients. Similarly to previous works on airborne wind energy, a linear relation between the derivative of the course angle and the steering input was found. The analysis of the on-ground tensiometers and the on-board load cells revealed a variable time delay up to 0.2 s between both measurements. The work shows that the testbed and its instruments are suitable to investigate the effect of tether sagging and to develop and test controllers for airborne wind energy systems.
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CC1: 'Comment on wes-2024-170', Joe Faust, 10 Dec 2024
EnergyKiteSystems.net will certainly be interested in your progress. Please forward your notes to joefaust333@gmail.com
Thank you,
Joe Faust
Disclaimer: this community comment is written by an individual and does not necessarily reflect the opinion of their employer.Citation: https://doi.org/10.5194/wes-2024-170-CC1 -
EC1: 'Reply on CC1', Roland Schmehl, 10 Dec 2024
Dear Joe Faust,
Thank you for your interest in this work. The journal implements an Interactive Public Peer Review, and all communication between authors, the general public and the assigned peer reviewers is logged here and preserved for transparency. If accepted for publication, the final manuscript will later be posted here, together with the peer reviews and the author's responses, each assigned separate DOIs. You can find more information about this here: https://www.wind-energy-science.net/peer_review/interactive_review_process.html
Best regards,
Roland Schmehl
Handling Associate EditorCitation: https://doi.org/10.5194/wes-2024-170-EC1
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EC1: 'Reply on CC1', Roland Schmehl, 10 Dec 2024
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RC1: 'Comment on wes-2024-170', Anonymous Referee #1, 23 Dec 2024
In this paper, the authors presented the system architecture of their ground station AWE testbed, followed by some practical discussions on tuning the controller to track a figure of eight motion. The paper is well-written and provides some interesting insights for further research.
MINOR COMMENTS
1. The discussions surrounding the individual elements of each flight (lines 251-265) are a bit hard to follow. This makes it difficult to follow subsequent discussions, which are based on lines 251-265. I suggest keeping figure 5 but adding two more annotated figures for flights A and B, then expanding lines 251-265 to describe the components of flight A and flight B trajectories separately.
2. The authors mentioned the addition of a third tether line for pitch control, but there's not much (if any) discussion on the improved pitch dynamics. I assume that the window to do pitch dynamics flight tests has passed. If so, some comments on how the third line can improve flying qualities and/or direction for future studies regarding this would be appreciated.
TECHNICAL COMMENTS
Some suggested typo/grammar fixes:
1. Line 83: we refer to CL and CR as the points where
2. Line 134: please format the reference
3. Line 291: same order of magnitude as
4. Line 308: and as noted in the first paragraph
5. Line 321: double use if it/its. Unsure which one is which.
6. Line 331: Young's
Citation: https://doi.org/10.5194/wes-2024-170-RC1 - AC1: 'Reply on RC1', Francisco de los Ríos Navarrete, 10 Feb 2025
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RC2: 'Comment on wes-2024-170', Anonymous Referee #2, 25 Jan 2025
- AC2: 'Reply on RC2', Francisco de los Ríos Navarrete, 10 Feb 2025
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RC3: 'Comment on wes-2024-170', Anonymous Referee #3, 31 Jan 2025
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Summary
=============The paper presents the significant extension of an existing small-scale test bed for airborne wind energy.
The choice of wing structure is a rigid-framed delta kite, a concept which is also being pursued by the copmany Enerkite, one of the more advanced AWE companies. The kite is controlled from a ground station via three lines, allowing steering and pitching of the wing and reeling in and out. Next to the advancements with respect to hardware (adding the third line, line tensionmeters and load cells), the main contribution is the development and experimental validation of a PID-controller based on a mixed waypoint/continuous reference path. The flight experiment data are then utilized to develop models for some of the system subcomponents.The paper is written very well and provides an extensive overview of the existing literature and state-of-the-art. Overall, it is a novel and interesting addition to the existing body of experimental AWE work and can provide a useful resource for practitioners and researchers alike.
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Minor comments:
===============- Some more context could be provided to motivate the choice of control strategy. Why was this specific strategy chosen, what are its advantages and limitations, in particular in comparison with existing (published) strategies for delta kites?
- While the third kite line for pitch control (as well as the option for reeling in and out) is mentioned as a contribution of the paper, I could not find a corresponding block in the control block diagram (Fig. 4). It would therefore be useful to devote a paragraph outlining a possible extension of the controller to allow for these extra built-in features of the hardware setup.
Citation: https://doi.org/10.5194/wes-2024-170-RC3 - AC3: 'Reply on RC3', Francisco de los Ríos Navarrete, 10 Feb 2025
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