uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Theoretical and Experimental Analysis of Operational Wave Energy Converters
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave Energy)ORCID iD: 0000-0002-4882-4151
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 [en]
ocean wave energy, WEC, permanent magnet, linear generator, closed stator slots, offshore experiments
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-274635ISBN: 978-91-554-9460-5 (print)OAI: oai:DiVA.org:uu-274635DiVA: diva2:897125
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
List of papers
1. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
Show others...
2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, 50-54 p.Article in journal (Refereed) Published
Abstract [en]

The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
2. Experimental results of rectification and filtration from an offshore wave energy system
Open this publication in new window or tab >>Experimental results of rectification and filtration from an offshore wave energy system
Show others...
2009 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 34, no 5, 1381-1387 p.Article in journal (Refereed) Published
Abstract [en]

The present paper presents results from a wave energy conversion that is based on a direct drive linear generator. The linear generator is placed on the seabed and connected to a buoy via a rope. Thereby, the natural wave motion is transferred to the translator by the buoy motion. When using direct drive generators, voltage and current output will have varying frequency and varying amplitude and the power must be converted before a grid connection. The electrical system is therefore an important part to study in the complete conversion system from wave energy to grid connected power. This paper will bring up the first steps in the conversion: rectification and filtration of the power. Both simulation studies and offshore experiments have been made. The results indicate that this kind of system works in a satisfactory way and a smooth DC power can be achieved with one linear generator.

Keyword
Wave energy conversion, Electric rectifiers, Energy conversion, Experiments, Porous materials, Power takeoffs, Takeoff
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112941 (URN)10.1016/j.renene.2008.09.010 (DOI)000263608500026 ()
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
3. Study of aWave Energy Converter Connected to a Nonlinear Load
Open this publication in new window or tab >>Study of aWave Energy Converter Connected to a Nonlinear Load
Show others...
2009 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 2, 123-127 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents experimental results from a wave energy converter (WEC) that is based on a linear generator connected to a rectifier and filter components. The converter-filter system is installed onshore, while the linear wave generator operates offshore a few kilometers from the Swedish west coast. The power from the generator has been rectified with a diode bridge and then filtered using a capacitive filter. Performance of the whole conversion system was studied using resistive loads connected across the filter. The aim was to investigate the operational characteristics of the generator while supplying a nonlinear load. By changing the value of the resistive component of the load, the speed of the translator can be changed and so also the damping of the generator. The power absorbed by the generator was studied at different sea states as well. The observations presented in this paper could be beneficial for the design of efficient wave energy conversion systems.

Keyword
ocean waves
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112947 (URN)10.1109/JOE.2009.2015021 (DOI)000266245600004 ()
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
4. Experimental Results From an Offshore Wave Energy Converter
Open this publication in new window or tab >>Experimental Results From an Offshore Wave Energy Converter
Show others...
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.

Keyword
ocean wave power, linear generators, conversion systems, experimental results
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-133599 (URN)10.1115/1.4001443 (DOI)000283325300003 ()
Available from: 2010-11-15 Created: 2010-11-11 Last updated: 2017-12-12Bibliographically approved
5. Design proposal of electrical system for linear generator wave power plants
Open this publication in new window or tab >>Design proposal of electrical system for linear generator wave power plants
Show others...
2009 (English)In: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS, IEEE , 2009, 4180-4185 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes an electrical system layout for a wave power plant connecting linear generators to the grid. The electrical power out from the wave energy converters must be converted before they can be connected to the grid. The conversion is carried out in marine substations that will be placed on the seabed.

The paper presents experimental power data from a wave energy converter that has been in operation at the Lysekil research site since March 2006. Moreover, results and analyses from experiments and simulations from tests with the generator connected to a rectifier and filter are presented. A simulation is made to show the difference between having the generator connected to a linear load and a nonlinear load, which would be the case when the generator is connected to the grid.

Place, publisher, year, edition, pages
IEEE, 2009
Keyword
electrical system layout, linear generator wave power plants, marine substations, wave energy converters
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112956 (URN)10.1109/IECON.2009.5414903 (DOI)000280762001321 ()978-1-4244-4648-3 (ISBN)978-1-4244-4650-6 (ISBN)
Conference
35th Annual Conference of the IEEE-Industrial-Electronics-Society (IECON 2009), Porto, PORTUGAL, NOV 03-05, 2009
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
6. Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site
Open this publication in new window or tab >>Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site
Show others...
2015 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 77, 9-14 p.Article in journal (Refereed) Published
Abstract [en]

Power generation from wave power has a large potential to contribute to our electric energy production, and today, many wave power projects are close to be commercialized. However, one key issue to solve for many projects is to decrease the cost per installed kW. One way to do this is to investigate which parameters that have a significant impact on the wave energy converters (WEC) performance. In this paper, experimental results on power absorption from a directly driven point absorbing WEC are presented. The experiments have been carried out at the Lysekil research site in Sweden. To investigate the performance of the WEC, the absorbed power and the speed of the translator are compared. The result confirms that the buoy size and the translator weight have a large impact on the power absorption from the generator. By optimizing the buoy size and translator weight, the WEC is believed to produce power more evenly over the upward and downward cycle. Moreover, to predict the maximum power limit during normal operation, a simulation model has been derived. The results correlates well with experimental data during normal operation. 

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-238267 (URN)10.1016/j.renene.2014.11.050 (DOI)000349504800002 ()
Available from: 2014-12-11 Created: 2014-12-11 Last updated: 2017-12-05Bibliographically approved
7. Lysekil Research Site, Sweden: A status update
Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
Show others...
2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-160039 (URN)
Conference
9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
8. A Switchgear
Open this publication in new window or tab >>A Switchgear
2011 (English)Patent (Other (popular science, discussion, etc.))
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-238262 (URN)
Patent
WO2011/031198
Available from: 2014-12-11 Created: 2014-12-11 Last updated: 2016-04-19
9. Detailed Study of Closed Stator Slots for a Direct-Driven Synchronous Permanent Magnet Linear Wave Energy Converter
Open this publication in new window or tab >>Detailed Study of Closed Stator Slots for a Direct-Driven Synchronous Permanent Magnet Linear Wave Energy Converter
2014 (English)In: Machines, Vol. 2, no 1, 73-86 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this paper is to analyze how a permanent magnet linear generator for wave power behaves when the stator slots are closed. The usual design of stator geometry is to use open slots to maintain a low magnetic leakage flux between the stator teeth. By doing this, harmonics are induced in the magnetic flux density in the air-gap due to slotting. The closed slots are designed to cause saturation, to keep the permeability low. This reduces the slot harmonics in the magnetic flux density, but will also increase the flux leakage between the stator teeth. An analytical model has been created to study the flux through the closed slots and the result compared with finite element simulations. The outcome shows a reduction of the cogging force and a reduction of the harmonics of the magnetic flux density in the air-gap. It also shows a small increase of the total magnetic flux entering the stator and an increased magnetic flux leakage through the closed slots.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-237484 (URN)10.3390/machines2010073 (DOI)
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2016-03-09
10. Performance study of linear permanentmagnet synchronous generators for wave power with closed stator slots
Open this publication in new window or tab >>Performance study of linear permanentmagnet synchronous generators for wave power with closed stator slots
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-274634 (URN)
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2016-03-09
11. Study of the operation characteristics of a point absorbing direct driven permanent magnet linear generator deployed in the Baltic Sea
Open this publication in new window or tab >>Study of the operation characteristics of a point absorbing direct driven permanent magnet linear generator deployed in the Baltic Sea
Show others...
2016 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 8, 1204-1210 p.Article in journal (Refereed) Published
Abstract [en]

To experimentally study how a wave energy converter (WEC) behaves when parameters such as weight on the translator and buoy volume are changing is of significant importance when trying to optimise the WEC system. This study presents results from a WEC deployed at the Baltic Sea near the island of Åland. Compared with earlier experiments, the weight on the translator has been significantly increased to suit the buoy volume. Experimental results show that the power output between the upward and the downward motions are comparable up to the maximum speed for the downward motion of the translator. To study the speed of the translator in downward direction a model has been derived. The model has also been used to study the impact of having a changing active area. Moreover, finite element (FE) simulations done on the generator have been compared with experimental data and show a good agreement, but at high speeds of the translator the FE simulations start to deviate from the experiments.

Keyword
Finite element method, Hydroelectric generators, Permanent magnets, Wave energy conversion Direct-driven, FE-simulation, Finite element simulations, Maximum speed, Operation characteristic, Permanent-magnet linear generators, Power out put, Wave energy converters
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-274633 (URN)10.1049/iet-rpg.2015.0413 (DOI)000384016100018 ()2-s2.0-84986915943 (Scopus ID)
Funder
EU, European Research Council
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2017-11-30Bibliographically approved
12. A wave power unit
Open this publication in new window or tab >>A wave power unit
Show others...
2009 (English)Patent (Other (popular science, discussion, etc.))
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-140112 (URN)
Patent
WO 2010/085188 (2010-07-29)
Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2016-04-14Bibliographically approved

Open Access in DiVA

fulltext(1801 kB)411 downloads
File information
File name FULLTEXT01.pdfFile size 1801 kBChecksum SHA-512
a72d72a86cb88c21ddb43de002d28c404acbfe2df718d216010e4c3c06d126ab06320ad8f796f1e63132f8f0f2fcdac053168019241970cc0b764c5e6add95dc
Type fulltextMimetype application/pdf
Buy this publication >>

Authority records BETA

Lejerskog, Erik

Search in DiVA

By author/editor
Lejerskog, Erik
By organisation
Electricity
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 411 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1766 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf