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Experimental Results From an Offshore Wave Energy Converter
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
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2010 (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 132, no 4, 041103- p.Article in journal (Refereed) Published
Abstract [en]

An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.

Place, publisher, year, edition, pages
2010. Vol. 132, no 4, 041103- p.
Keyword [en]
ocean wave power, linear generators, conversion systems, experimental results
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-133599DOI: 10.1115/1.4001443ISI: 000283325300003OAI: oai:DiVA.org:uu-133599DiVA: diva2:370043
Available from: 2010-11-15 Created: 2010-11-11 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Electrical Systems for Wave Energy Conversion
Open this publication in new window or tab >>Electrical Systems for Wave Energy Conversion
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several technologies on how to convert the energy in the ocean waves into electric energy. The wave energy converter (WEC) presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power.

To convert and interconnect the power from the generators, marine substations are used. The marine substations are placed on the seabed and convert the fluctuating AC from the generators into an AC suitable for grid connection.

The work presented in the thesis focuses on the first steps in the electric energy conversion, converting the voltage out from the generators into DC, which have an impact on the WEC's ability to absorb and produce power. The purpose has been to investigate how the generator will operate when it is subjected to different load cases and to obtain guidelines on how future systems could be improved. Offshore experiments and simulations have been done on full scale generators connected to four different loads, i.e. one linear resistive load and three different non-linear loads representing different cases for grid connected WECs.

The results show that the power can be controlled and optimized by choosing a suitable system for the WEC. It is not obvious which kind of system is the most preferable, since there are many different parameters that have an impact on the system performance, such as the size of the buoy, how the generator is designed, the number of WECs, the highest allowed complexity of the system, costs and so on. Therefore, the design of the electrical system should preferably be carried out in parallel with the design of the WEC in order to achieve an efficient system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 104 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 797
Keyword
Wave power, direct driven linear generators, electrical systems, non-linear loads
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-140116 (URN)978-91-554-7982-4 (ISBN)
Public defence
2011-02-18, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Note

Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 727

Available from: 2011-01-28 Created: 2011-01-04 Last updated: 2013-05-17Bibliographically approved
2. Buoy and Generator Interaction with Ocean Waves: Studies of a Wave Energy Conversion System
Open this publication in new window or tab >>Buoy and Generator Interaction with Ocean Waves: Studies of a Wave Energy Conversion System
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed.

This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values.

The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly.

The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong.

As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 872
Keyword
Wave power, Measurement systems, Marine technology, Energy conversion, Renewable energy, Energy absorption, Wave resource, Oceanic engineering, Linear generators, Point absorbers, Sea trials, Camera systems, Accelerometers, Offshore experiments
National Category
Energy Engineering Marine Engineering Energy Systems Ocean and River Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-160085 (URN)978-91-554-8192-6 (ISBN)
Public defence
2011-12-02, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-11-11 Created: 2011-10-14 Last updated: 2012-01-09Bibliographically approved
3. Linear wave energy converter: Study of electromagnetic design
Open this publication in new window or tab >>Linear wave energy converter: Study of electromagnetic design
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis presents results from synchronous linear wave energy converters developed at Uppsala University. A study is done on closed stator slots and a study presenting offshore data focusing on the power absorption from a wave energy converter (WEC). The first step in studying the closed slots has been done during no-load, to study the magnetic flux path from the permanent magnets and to study the forces in the linear generator. The initial studies show a reduction in cogging force and a reduction in harmonics in the magnetic flux density in the air-gap. It also shows an increase of the total flux entering the stator and an increase in flux leakage. The study has been done with FEM simulations and compared with analytical calculations.

The second study was done to investigate the power absorption of a WEC in upward and downward motion in relation to the volume of the buoy and mass of the system. The experimental results were compared with a static model focusing on the limit in the absorption. As expected from the model, the WEC absorbs more energy in the upward direction. Also indications of snatch load were observed. Within this thesis, results from a comparison study between two WECs with almost identical electrical properties and the same volume of the buoy, but with different height and diameter have been presented. Moreover, experimental studies including the conversion step between AC to DC have been done.

The work done in this thesis is a part of a larger wave power project at Uppsala University. Where everything between the energy absorption from the waves to the connection to the electrical grid is studied. The project has a test-site at the west coast of Sweden near the town Lysekil, where wave energy research has been carried out since 2004.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2014. 62 p.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 335-14L
Keyword
Wave energy, permanent magnets, linear generator, closed stator slots, offshore experiments
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-237522 (URN)
Presentation
(English)
Opponent
Supervisors
Funder
Swedish Research Council, 2009-3417
Available from: 2014-12-11 Created: 2014-12-03 Last updated: 2014-12-11Bibliographically approved
4. Theoretical and Experimental Analysis of Operational Wave Energy Converters
Open this publication in new window or tab >>Theoretical and Experimental Analysis of Operational Wave Energy Converters
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies wave energy converters developed at Uppsala University. The wave energy converters are of point absorbing type with direct driven linear generators. The aim has been to study generator design with closed stator slots as well as offshore experimental studies.

By closing the stator slots, the harmonic content in the magnetic flux density is reduced and as a result the cogging forces in the generator are reduced as well. By reducing these forces, the noise and vibrations from the generator can be lowered. The studies have shown a significant reduction in the cogging forces in the generator. Moreover, by closing the slots, the magnetic flux finds a short-cut through the closed slots and will lower the magnetic flux linking the windings.

The experimental studies have focused on the motion of the translator. The weight of the translator has a significant impact on the power absorption, especially in the downward motion. Two different experiments have been studied with two different translator weights. The results show that with a higher translator weight the power absorption is more evenly produced between the upward and downward motion as was expected from the simulation models. Furthermore, studies on the influence of the changing active area have been conducted which show some benefits with a changing active area during the downward motion. The experimental results also indicate snatch-loads for the wave energy converter with a lower translator weight.

Within this thesis results from a comparative study between two WECs with almost identical properties have been presented. The generators electrical properties and the buoy volumes are the same, but with different buoy heights and diameters. Moreover, experimental studies including the conversion from AC to DC have been achieved.

The work in this thesis is part of a larger wave power project at Uppsala University. The project studies the whole process from the energy absorption from the waves to the connection to the electrical grid. The project has a test-site at the west coast of Sweden near the town of Lysekil, where wave energy systems have been studied since 2004.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1339
Keyword
ocean wave energy, WEC, permanent magnet, linear generator, closed stator slots, offshore experiments
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-274635 (URN)978-91-554-9460-5 (ISBN)
Public defence
2016-03-11, Häggsalen, Ångström, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2016-02-18 Created: 2016-01-24 Last updated: 2016-03-09

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Boström, CeciliaLejerskog, ErikTyrberg, SimonSvensson, OlleWaters, RafaelSavin, AndrejLeijon, Mats

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