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
Experimental results of rectification and filtration from an offshore wave energy system
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.
Show others and affiliations
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.

Place, publisher, year, edition, pages
2009. Vol. 34, no 5, 1381-1387 p.
Keyword [en]
Wave energy conversion, Electric rectifiers, Energy conversion, Experiments, Porous materials, Power takeoffs, Takeoff
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-112941DOI: 10.1016/j.renene.2008.09.010ISI: 000263608500026OAI: oai:DiVA.org:uu-112941DiVA: diva2:289083
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
In thesis
1. Ocean Wave Energy: Underwater Substation System for Wave Energy Converters
Open this publication in new window or tab >>Ocean Wave Energy: Underwater Substation System for Wave Energy Converters
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with a system for operation of directly driven offshore wave energy converters. The work that has been carried out includes laboratory testing of a permanent magnet linear generator, wave energy converter mechanical design and offshore testing, and finally design, implementation, and offshore testing of an underwater collector substation. Long-term testing of a single point absorber, which was installed in March 2006, has been performed in real ocean waves in linear and in non-linear damping mode. The two different damping modes were realized by, first, a resistive load, and second, a rectifier with voltage smoothing capacitors and a resistive load in the DC-link. The loads are placed on land about 2 km east of the Lysekil wave energy research site, where the offshore experiments have been conducted. In the spring of 2009, another two wave energy converter prototypes were installed. Records of array operation were taken with two and three devices in the array. With two units, non-linear damping was used, and with three units, linear damping was employed. The point absorbers in the array are connected to the underwater substation, which is based on a 3 m3 pressure vessel standing on the seabed. In the substation, rectification of the frequency and amplitude modulated voltages from the linear generators is made. The DC voltage is smoothened by capacitors and inverted to 50 Hz electrical frequency, transformed and finally transmitted to the on-shore measuring station. Results show that the absorption is heavily dependent on the damping. It has also been shown that by increasing the damping, the standard deviation of electrical power can be reduced. The standard deviation of electrical power is reduced by array operation compared to single unit operation. Ongoing and future work include the construction and installation of a second underwater substation, which will connect the first substation and seven new WECs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 114 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 711
Keyword
wave energy, wave power, wave energy converter, direct-drive, permanent magnet linear generator, point absorber, array, farm, park, offshore, marine, substation, electrical transmission system
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-112915 (URN)978-91-554-7713-4 (ISBN)
Public defence
2010-03-05, Ångströmlaboratoriet, Polhemsalen, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2010-02-12 Created: 2010-01-22 Last updated: 2013-07-31Bibliographically approved
2. 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
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

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Boström, CeciliaLejerskog, ErikStålberg, MagnusLeijon, Mats

Search in DiVA

By author/editor
Boström, CeciliaLejerskog, ErikStålberg, MagnusLeijon, Mats
By organisation
Electricity
In the same journal
Renewable energy
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 758 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