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Theory and Simulations of an End Stop Solution in a Linear Wave Power Generator
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
(English)Manuscript (preprint) (Other academic)
National Category
Other Civil Engineering
Identifiers
URN: urn:nbn:se:uu:diva-207205OAI: oai:DiVA.org:uu-207205DiVA: diva2:647079
Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2014-09-18Bibliographically approved
In thesis
1. Full Scale Applications of Permanent Magnet Electromagnetic Energy Converters: From Nd2Fe14B to Ferrite
Open this publication in new window or tab >>Full Scale Applications of Permanent Magnet Electromagnetic Energy Converters: From Nd2Fe14B to Ferrite
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents research regarding a full scale linear ferrite permanent magnet generator, installed in a wave energy conversion system. The ferrite based magnetic circuit, supplementing the previous utilized Nd2Fe14B-magnet design, is designed with an electromagnetic numerical simulation tool, where the model is derived from Maxwell’s equations. The full scale design is, known to the author, the first developed linear ferrite based machine. The material change in the magnetic circuit required different mechanical solutions of the generator. The fundamental, primary theory and reasoning behind the new mechanical design is here presented, where sustainability, economy and production have been in focus and affected the final design. Two versions of the generator have been assembled and deployed at the projects experimental site on the Swedish west coast, and three more are under construction, planned to be installed during the autumn of 2013.  

Further, the thesis presents an electric conversion circuit based on the electric resonance phenomena. Full scale experimental results present a successfully achieved electric resonance between the linear wave energy generator and external circuit.

Finally, research regarding a two pole permanent magnet motor for an electrical vehicle is presented. Detailed analytical and numerical calculations are utilized to investigate the losses in the machine over a wide frequency interval. The results indicate the possibility of an increased efficiency of electrical motors in electrical vehicle system and argue for elimination of the gearbox. The system total efficiency and mechanical stability can thereby be increased.   

The work concerning the wave energy converter is a part of a larger project, the Lysekil Wave Power Project, developed by a research group at Uppsala University, whereas the work concerning the electric motor so far has been carried out as an individual project. However, a future goal is to integrate the research on the electric motor for electric vehicles with ongoing research regarding a flywheel based electric driveline for an All Electric Propulsion System.      

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1074
National Category
Water Engineering
Identifiers
urn:nbn:se:uu:diva-207280 (URN)978-91-554-8752-2 (ISBN)
Public defence
2013-10-25, Polhemsalen, Ångströmslaboratoriet, Regementsvägen 1, Uppsala, 15:55 (English)
Opponent
Supervisors
Available from: 2013-10-04 Created: 2013-09-11 Last updated: 2014-01-23
2. Buoy Geometry, Size and Hydrodynamics for Power Take Off Device for Point Absorber Linear Wave Energy Converter
Open this publication in new window or tab >>Buoy Geometry, Size and Hydrodynamics for Power Take Off Device for Point Absorber Linear Wave Energy Converter
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wave energy converters of point absorber type have been developed and constructed. Full scale experiments have been carried out at sea and electricity has been successfully delivered. Linear permanent magnet generators together with a subsea substation and buoys of various geometric shapes have been investigated theoretically and experimentally. The design has in large extent an electronic approach, keeping the mechanical part of it as simple as possible, due to the long life span and reliability of electric components.

Because of the nature of a linear generator, the internal translator with permanent magnets has a limited stroke length which will be reached when the buoy is exposed to large wave heights. Internal springs at the top and bottom of the generator prevent the translator from hitting the generator hull. Inertial forces due to the mass and velocity of the translator and the buoy and its heave added mass compresses the spring. The added mass is a rather large part of the total moving mass. Simulations of a converter with a vertical cylindrical buoy and with a toroidal buoy were conducted, as well as real sea experiments with converters with cylindrical buoys of two different sizes and a toroidal buoy. The overloads are likely to affect the design and service life of the generator, the buoy and the wire which interconnects them.

Buoy shapes with as much excitation force as possible and as little heave added mass as possible were sought. A toroidal buoy caused less overloads on the generator at sea states with short wave periods and relatively large wave height, but for sea states with very long wave periods or extremely high waves, the magnitude of the overloads was mainly determined by the maximum displacement of the buoy.

Snap loads on the interconnecting wire, as the slack wire tensed up after a very deep wave trough, were found to be greater but of the same order of magnitude as forces during the rest of the wave cycle.

During a 4 day period at various wave conditions, two converters with cylindrical buoys proved efficiency between 11.1 % and 24.4 %. The larger buoy had 78 % larger water plane area than the other buoy which resulted in 11 % more power production. Short wave period was beneficial for the power production.

Infinite frequency heave added mass was measured for a cylindrical buoy at real sea and found to be greater than the linearly calculated theoretical added mass.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 71 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1130
Keyword
point absorber, wave, energy, converter, ocean, wec, toroidal, buoy, torus, cylindrical, cylinder, experiment, full scale, trial, sea, energy, renewable
National Category
Energy Engineering Fluid Mechanics and Acoustics
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-220344 (URN)978-91-554-8902-1 (ISBN)
Public defence
2014-04-28, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-04-04 Created: 2014-03-13 Last updated: 2014-09-18Bibliographically approved

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Gravråkmo, HalvarLeijon, Mats

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