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Experimental results from the Lysekil Wave Power Research Site
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave Power)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source.

The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state.

The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land.

Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis.

The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter.

Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line.

Abstract [sv]

Den här avhandlingen berättar om hur experimenten vid Lysekils forskningsområde för vågkraft har utförts. Insamlade mätdata har använts för att verifiera teoretiska samband som modulerats vid Elektricitetslära, Uppsala universitet. De teoretiska och praktiska resultaten har visat på att vågkraft har förutsättningarna att implementeras som en hållbar framtida energikälla. Intressanta mätmetoder har utvecklas och påfrestningarna  på utrustningin och dess samband med medel effekten har studerats.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 101 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 957
Keyword [en]
Wave power, Lysekil, Marine Substation, Offshore measurement, strain gauge, lateral force, Invlination and azimuth angles, Wave energy converter, Temperature measurements, Inverter, Energy, Control sustem, CompactRIO, Vågkraft, Mätteknik, Styrsystem, Lysekil
National Category
Marine Engineering Energy Systems Other Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering Control Engineering
Research subject
Engineering Science
Identifiers
URN: urn:nbn:se:uu:diva-179098ISBN: 978-91-554-8433-0 (print)OAI: oai:DiVA.org:uu-179098DiVA: diva2:544603
Public defence
2012-09-28, Polhem Å 10134, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Projects
Lysekils projektet
Funder
Swedish Research Council, grant no. 621-2009-3417
Available from: 2012-09-05 Created: 2012-08-07 Last updated: 2013-01-22
List of papers
1. Experiments at Islandsberg on the west coast of Sweden in preparation of the construction of a pilot wave power plant
Open this publication in new window or tab >>Experiments at Islandsberg on the west coast of Sweden in preparation of the construction of a pilot wave power plant
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2005 (English)In: 6th EWTEC conference, Glasgow, August 28-September 3, 2005, 5 sid- p.Conference paper, Published paper (Other scientific)
Identifiers
urn:nbn:se:uu:diva-75974 (URN)
Available from: 2006-02-22 Created: 2006-02-22 Last updated: 2012-09-07
2. Experimental results from sea trials of an offshore wave energy system
Open this publication in new window or tab >>Experimental results from sea trials of an offshore wave energy system
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 3, 034105- p.Article in journal (Refereed) Published
Abstract [en]

A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and significant insights discovered. Energy absorption dependency on load as well as output voltage and power is demonstrated. It is shown that great overload capability of the directly driven linear generator is critical, and indicated that, for resistive loads, optimal load does not vary with wave climate. Future grid supplying energy production would necessitate parks of wave power plants in order to reduce power fluctuations.

Keyword
High-current and high-voltage technology: power systems; power transmission lines and cables, Electric motors
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-95683 (URN)10.1063/1.2432168 (DOI)000243582400105 ()
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
3. Wave power absorption: Experiments in open sea and simulation
Open this publication in new window or tab >>Wave power absorption: Experiments in open sea and simulation
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 8, 084910-084910-5 p.Article in journal (Refereed) Published
Abstract [en]

A full scale prototype of a wave power plant based on a direct drive linear generator driven by a point absorber has been installed at the west coast of Sweden. In this paper, experimentally collected data of energy absorption for different electrical loads are used to verify a model of the wave power plant including the interactions of wave, buoy, generator, and external load circuit. The wave-buoy interaction is modeled with linear potential wave theory. The generator is modeled as a nonlinear mechanical damping function that is dependent on piston velocity and electric load. The results show good agreement between experiments and simulations. Potential wave theory is well suited for the modeling of a point absorber in normal operation and for the design of future converters. Moreover, the simulations are fast, which opens up for simulations of wave farms.

Keyword
Hydroelectric, hydrothermal, geothermal and wind power, Ocean energy extraction, Ocean waves and oscillations
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-95684 (URN)10.1063/1.2801002 (DOI)000250589300146 ()
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
4. Wave Energy from the North Sea: Experiences from the Lysekil Research Site
Open this publication in new window or tab >>Wave Energy from the North Sea: Experiences from the Lysekil Research Site
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2008 (English)In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, 221-240 p.Article, review/survey (Refereed) Published
Abstract [en]

This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

Keyword
Wave power, Renewable energy, Sea trial, Linear generator, Point absorber, Environmental impact
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-107215 (URN)10.1007/s10712-008-9047-x (DOI)000260967900002 ()
Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2017-12-13Bibliographically approved
5. 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
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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
6. Description of the control and measurement system used in the Low Voltage Marine Substation at the Lysekil research site
Open this publication in new window or tab >>Description of the control and measurement system used in the Low Voltage Marine Substation at the Lysekil research site
2009 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Uppsala, Sweden: , 2009
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113300 (URN)
Conference
EWTEC09
Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2016-04-14Bibliographically approved
7. 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
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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: 2017-12-12Bibliographically approved
8. Laboratory experimental verification of a marine substation
Open this publication in new window or tab >>Laboratory experimental verification of a marine substation
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2009 (English)In: The 8th European Wave and Tidal Energy Conference EWTEC 2009: book of abstracts, Uppsala, 2009, 51-58 p.Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Uppsala: , 2009
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112952 (URN)
Conference
EWTEC09, Uppsala, Sweden 7-10 September 2009
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
9. 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
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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
10. Determining the service life of a steel wire under a working load in the Wave Energy Converter (WEC)
Open this publication in new window or tab >>Determining the service life of a steel wire under a working load in the Wave Energy Converter (WEC)
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2009 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Honolulu, Hawaii: , 2009
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113297 (URN)
Conference
Conference on Ocean, Offshore and Arctic Engineering (OMAE 2009)
Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2016-04-14Bibliographically approved
11. Offshore underwater substation for wave energy converter arrays
Open this publication in new window or tab >>Offshore underwater substation for wave energy converter arrays
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2010 (English)In: IET Renewable Power Generation, ISSN 1752-1416, Vol. 4, no 6, 602-612 p.Article in journal (Refereed) Published
Abstract [en]

In this study, the design, construction, deployment and operation of an offshore underwater substation is discussed. The seabed placed substation interconnects three linear generator wave energy converters (WECs) at the Swedish Lysekil wave energy research site. The power from the WECs fluctuates because of their direct-driven topology. The generator voltage has varying electrical frequency and amplitude. To reduce the fluctuations, the individual voltages of the WECs are rectified and the power is added on a common DC-bus in the substation. The voltage is inverted, transformed and power is transmitted to an on-shore resistive load. The substation was retrieved on two occasions since the deployment in the spring of 2009. The functionality of the substation is validated by comparing voltage and current wave forms from Simulink with measured results from laboratory experiments. In addition, a sample of results from real offshore operation is illustrated and discussed. With a proportional-integral-derivative (PID)-regulator in the inverter control, the small fluctuations in the DC-bus voltage could be minimised. However, this would reduce the energy storage capability of the DC-link smoothing capacitors.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-112954 (URN)10.1049/iet-rpg.2009.0180 (DOI)000284511300013 ()
Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-18Bibliographically approved
12. Experimental results from an offshore wave energy converter
Open this publication in new window or tab >>Experimental results from an offshore wave energy converter
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2008 (English)In: Volume 6: Nick Newman Symposium on Marine Hydrodynamics; Yoshida and Maeda Special Symposium on Ocean Space Utilization; Special Symposium on Offshore Renewable Energy, 2008, 653-657 p.Conference paper, Published paper (Refereed)
Abstract [en]

Anoffshore wave energy converter (WEC) was successfully launched at theSwedish west coast in the middle of March 2006. TheWEC is based on a permanent magnet linear generator locatedon the ocean floor driven by a point absorber. Ameasuring station has been installed on a nearby island whereall measurements and experiments on the WEC have been carriedout. The output voltage from the generator fluctuates both inamplitude and frequency and must therefore be converted to enablegrid connection. In order to study the voltage conversion, themeasure station was fitted with a six pulse diode rectifierand a capacitive filter during the autumn of 2006. Theobject of this paper is to present a detailed descriptionof the existing wave energy system of the Islandsberg project.Special attention will be given to the power absorption bythe generator when it is connected to a non linearload

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97845 (URN)10.1115/OMAE2008-57415 (DOI)
Conference
ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering (OMAE2008) June 15–20, 2008 , Estoril, Portugal
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2016-04-12Bibliographically approved
13. Description of a torus shaped buoy for wave energy point absorber
Open this publication in new window or tab >>Description of a torus shaped buoy for wave energy point absorber
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2010 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-142504 (URN)
Conference
Renewable Energy 2010, 27 June - 2 July, Pacifico Yokohama, Japan
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2015-01-07Bibliographically approved
14. Wave Buoy and Translator Motions - On-Site Measurements and Simulations
Open this publication in new window or tab >>Wave Buoy and Translator Motions - On-Site Measurements and Simulations
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2011 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 36, no 3, 377-385 p.Article in journal (Refereed) Published
Abstract [en]

For a complete understanding of a wave energy conversion device, it is important to know how the proposed device moves in the water, how this motion can be measured, and to what extent the motion can be predicted or simulated. The magnitude and character of the motion has impacts on engineering issues and optimization of control parameters, as well as the theoretical understanding of the system. This paper presents real sea measurements of buoy motion and translator motion fora wave energy system using a linear generator. Buoy motion has been measured using two different systems: a land-based optical system and a buoy-based accelerometer system. The data have been compared to simulations from a Simulink model for the entire system. The two real sea measurements of buoy motion have been found to correlate well in the vertical direction, where the measured range of motion and the standard deviation of the position distributions differed with 3 and 4 cm, respectively. The difference in the horizontal direction ismore substantial. The main reason for this is that the buoy rotation about its axis of symmetry was not measured. However, used together the two systems give a good understanding of buoy motion. In a first comparison, the simulations show good agreement with the measured motion for both translator and buoy.

Keyword
Accelerometers, energy conversion, experimental results, image motion analysis, oceanic engineering, marine technology, wave power
National Category
Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-160072 (URN)10.1109/JOE.2011.2136970 (DOI)
Available from: 2012-01-09 Created: 2011-10-14 Last updated: 2017-12-08Bibliographically approved
15. Ocean wave energy absorption in response to wave period and amplitude: offshore experiments on a wave energy converter
Open this publication in new window or tab >>Ocean wave energy absorption in response to wave period and amplitude: offshore experiments on a wave energy converter
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2011 (English)In: IET Renewable Power Generation, ISSN 1752-1416, Vol. 5, no 6, 465-469 p.Article in journal (Refereed) Published
Abstract [en]

The ability of a wave energy converter to capture the energy of ocean waves has been studied in offshore experiments. This study covers 50 days during which the converter was subjected to ocean waves over a wide range of frequencies and amplitudes as well as three different electrical loads. The results present the wave energy converter??s energy absorption as a function of significant wave height, energy period and electrical load. It is shown that the power generated overall continues to increase with wave amplitude, whereas the relative absorption decreases towards the highest periods and amplitudes. The absorption reached a maximum of approximately 24% with the used combination of buoy, generator and electrical load. Absorption to cover for iron and mechanical losses has not been included. A brief study of the nature of the electromagnetic damping force has also been included in the study. The wave energy converter is of the technology that is being researched at Uppsala University and experimented on off the Swedish west coast at the Lysekil wave energy research site.

Place, publisher, year, edition, pages
IEEE Press, 2011
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-165034 (URN)10.1049/iet-rpg.2010.0124 (DOI)000303376900007 ()
Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2013-05-17Bibliographically approved
16. Lysekil Research Site, Sweden: A status update
Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
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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
17. Sensors and Measurements Inside the Second and Third Wave Energy Converter at the Lysekil Research Site.
Open this publication in new window or tab >>Sensors and Measurements Inside the Second and Third Wave Energy Converter at the Lysekil Research Site.
2011 (English)Conference paper, Published paper (Refereed)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-162252 (URN)
Conference
Conference
Available from: 2011-11-28 Created: 2011-11-28 Last updated: 2016-04-19
18. Temperature measurements in a linear generator and marine substation for wave power
Open this publication in new window or tab >>Temperature measurements in a linear generator and marine substation for wave power
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2012 (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 134, no 2, 021901- p.Article in journal (Refereed) Published
Abstract [en]

This paper analyzes temperature measurements acquired in the offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common dc-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. The first results of temperature measurements on substation components and on the stator of one of the linear generators are presented based on operation in linear and in nonlinear damping. The results indicate that there might be some convective heat transfer in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel in order to avoid heating from neighboring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding polyvinyl chloride cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the wave energy converter could be enhanced. Another suggested alteration is to lower the resistive losses by reducing the linear generator current density.

Keyword
convection, linear machines, machine insulation, machine windings, offshore installations, power convertors, stators, substations, temperature measurement, wave power generation
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-140113 (URN)10.1115/1.4004629 (DOI)000308596500021 ()
Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
19. A Set-Up of 7 Laser Triangulation Sensors and a Draw-Wire Sensor for Measuring Relative Displacement of a Piston Rod Mechanical Lead-Through Transmission in an Offshore Wave Energy Converter on the Ocean Floor
Open this publication in new window or tab >>A Set-Up of 7 Laser Triangulation Sensors and a Draw-Wire Sensor for Measuring Relative Displacement of a Piston Rod Mechanical Lead-Through Transmission in an Offshore Wave Energy Converter on the Ocean Floor
2012 (English)In: ISRN Renewable Energy, ISSN 2090-746X, Vol. 2012, 746865- p.Article in journal (Refereed) Published
Abstract [en]

A concept for offshore wave energy conversion is being developed at the Swedish Centre for Renewable Electric Energy Conversion at Uppsala University in Sweden. The wave energy converter (WEC) in focus contains a piston rod mechanical lead-through transmission for transmitting the absorbed mechanical wave energy through the generator capsule wall while preventing seawater from entering the capsule. A set-up of 7 laser triangulation sensors has been installed inside the WEC to measure relative displacement of the piston rod and its corresponding seal housing. A draw-wire sensor has also been set up to measure translator position and the axial displacement of the piston rod. The paper gives a brief introduction to the Lysekil research site, the WEC concept, and the direct drive of WEC prototype L2. A model of operation for the piston rod mechanical lead-through transmission is given. The paper presents sensor choice, configuration, adaptation, mounting, and measurement system calibration along with a description of the data acquisition system. Results from 60 s measurements of nominal operation two months apart with centered moving averages are presented. Uncertainty and error estimations with statistical analyses and signal-to-noise ratios are presented. Conclusions are drawn on the relative motions of the piston rod and the seal housing under normal operating conditions, and an assessment of the applicability of the measurement system is made.

Place, publisher, year, edition, pages
New York: Hindawi Publishing Corporation, 2012
Keyword
Wave energy, Laser, Sensor, Triangulation, Draw-wire, Piston rod, Transmission, Submerged, Offshore, Measurements, Mechanical lead-through.
National Category
Applied Mechanics Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-179099 (URN)10.5402/2012/746865 (DOI)
Projects
The Lysekil Wave Power Project
Available from: 2012-08-07 Created: 2012-08-07 Last updated: 2012-09-20Bibliographically approved
20. Estimation of Stress in the Inner Framework Structure of a Single Heaving Buoy Wave Energy Converter
Open this publication in new window or tab >>Estimation of Stress in the Inner Framework Structure of a Single Heaving Buoy Wave Energy Converter
2012 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 37, no 2, 309-317 p.Article in journal (Refereed) Published
Abstract [en]

This paper details a method for strain measurements in the inner framework structure of the single heaving buoy Wave Energy Converter (WEC). This type of the WEC consists of a linear direct drive generator placed on the sea floor and connected to the floating buoy through the connection line.

The study focuses on estimation of stress in the inner framework structure of the WEC using strain measurements in material. Stress in ocean structures is as important as maximum stress.The offshore experiment was made at the Lysekil research site a few kilometers from the Swedish west coast.Stresses had the maximum value when the translator hit an end stop. Interesting observations were made: compressive stress occurred in the framework crossbar at a sea state of 1.32 m waves, but both compressive and tensile stress occurred at a sea state of 3.2 m waves.

A computational procedure employs good results. Error estimation is calculated and represented. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.

Keyword
Calibration, Generators, Sea measurements, Strain, Strain measurement, Stress, Voltage measurement, ocean waves, stress measurement, tensile strength, wave power generation, WEC consists, compressive stress, floating buoy, inner framework structure, linear direct drive generator, single heaving buoy wave energy converter, strain measurements, stress estimation, tensile stress, Estimation of stress, wave energy converter (WEC)
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:uu:diva-159512 (URN)10.1109/joe.2012.2188614 (DOI)
Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2017-12-08Bibliographically approved
21. Azimuth-inclination angles and snatch load on a tight mooring system
Open this publication in new window or tab >>Azimuth-inclination angles and snatch load on a tight mooring system
2012 (English)In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 40, 40-49 p.Article in journal (Refereed) Published
Abstract [en]

A concept for wave energy conversion is being developed at the Swedish Center for Renewable Electric A Energy Conversion at the Angstrom Laboratory at Uppsala University, Sweden. This paper presents the results of offshore measurements where strain gauge sensors instrumented on the capsule of the WEC and a force transducer measuring line force from the floating buoy were used. A method for measurement and evaluation of the lateral force on the guiding system was developed. The experimental data allow us to define the inclination and azimuth angle between the generator and the floating buoy. The inclination angle is one of the key parameters for the design and the construction of the outer structure. It can be assumed that the inclination angle between the linear generator and the buoy with the stretched connection line did not exceed 8 at a sea state of 1.32 m waves. Snatch load between the buoy and the generator occur. This was obtained by a sudden jump of the inclination angle between the generator and the floating buoy. Moreover, the inclination and azimuth angle allow reproduction of the position of the floating buoy on the water surface.

Keyword
Tight mooring system, Offshore measurement, Strain gauge, Lateral force, Inclination and azimuth angles, Snatch load
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-171433 (URN)10.1016/j.oceaneng.2011.12.007 (DOI)000300521300004 ()
Available from: 2012-03-19 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
22. Experimental results from the operation of aggregated wave energy converters
Open this publication in new window or tab >>Experimental results from the operation of aggregated wave energy converters
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2012 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 6, no 3, 149-160 p.Article in journal (Refereed) Published
Abstract [en]

Wave energy comes in pulses and is unsuitable for direct conversion and transmission to the grid. One method to smooth the power is to deploy arrays of wave energy converters (WECs), the geometrical layout and damping optimisation of which many have studied analytically and numerically, but very few by experiments at sea. In this study, the standard deviation of electrical power as function of various parameters is investigated. Two offshore experiments have been conducted. During the longer run, three WECs were operated in linear damping during 19.7 days. It is shown that the standard deviation reduces with the number of WECs in the array up to three WECs. The reduction compared to single WEC operation was found here to be 30 and 80% with two and three WECs, respectively, as a mean for an arbitrary array member. It is found that in sea states above ~2 kW/m, the standard deviation is independent of sea state parameters. This is contradictory to a previous study on the same device. The results are, however, in accordance with numerical results of the SEAREV device but show larger reduction in standard deviation with number of WECs. This could be because of suboptimal damping conditions.

Keyword
offshore installations, power convertors, power grids, wave power generation, SEAREV device, WEC, aggregated wave energy converters operation, arbitrary array member, damping optimisation, direct conversion, direct transmission, electrical power standard deviation, geometrical layout, linear damping, offshore experiments, power grid, sea state parameters
National Category
Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-140114 (URN)10.1049/iet-rpg.2010.0234 (DOI)
Funder
StandUp
Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
23. Peak Force Measurements on a Cylindrical Buoy with Limited Elastic Mooring
Open this publication in new window or tab >>Peak Force Measurements on a Cylindrical Buoy with Limited Elastic Mooring
2014 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 39, no 2, 398-403 p.Article in journal (Refereed) Published
Abstract [en]

This paper investigates the line force of a moored floating buoy. The experiment was the first experiment made at the Swedish wave energy research area located close to Lysekil on the Swedish west coast. The Lysekil project is run by the Swedish Centre for Renewable Electric Energy Conversion at Uppsala University.                  The experimental set-up consists of a cylindrical buoy, with a diameter of 3 m and a height of 0.8 m. The buoy is moored with a line connected to a set of springs in parallel with a rope.

The rope in parallel with the springs represents the limited stroke length of a linear generator type wave energy converter. The measurement system consists of a force transducer between the buoy and the rope, a three axis accelerometer inside the buoy and a data logger remotely operated through the GSM network.

     The peak forces related to the significant wave height showed a trend of 33 kN/m. Trends was also calculated in 10 kN bins. The data could be used in fatigue simulations of similar devices. The result was used when dimensioning the wave energy converter that was installed in March 2006.

Keyword
Force measurement, Ocean technology, Peak Force, Offshore, Wave energy, Sea trial.
National Category
Other Mechanical Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-179102 (URN)10.1109/JOE.2013.2247825 (DOI)000334737500017 ()
Projects
The Lysekil Project
Available from: 2012-08-07 Created: 2012-08-07 Last updated: 2017-12-07Bibliographically approved
24. A Study of the Possible Power Extraction from a Point Absorbing Wave Energy Converter
Open this publication in new window or tab >>A Study of the Possible Power Extraction from a Point Absorbing Wave Energy Converter
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Today there exist several different ongoing wave power projects around the world. One of them is carried out by researchers at Uppsala University, Sweden. The concept is based on a point absorbing wave energy converter (WEC). A buoy is placed on the ocean surface and connected to a direct driven linear generator placed on the seabed. When the buoy moves with the waves, the moving part of the generator will move and a voltage is induced in the stator windings. The speed of the moving part will vary between zero and a peak value twice every wave period. The maximum speed and also the power depend on the wave height, the wave length and the damping of the generator. Moreover, the maximum speed of the real sea wave will be different for every wave period. Thus, the electrical system must be designed to handle the peak power that the generator generates even though the average power is significantly lower. This paper aims to investigate the difference between the peak power and mean power further. An analytical investigation of the possible maximum and mean power extraction of the WEC is performed. A comparison and discussion between the analytical results and results from experiments are presented. Moreover, the ongoing research activities at the university's research site are presented

 

Keyword
wave power; point absorber; linear generator, wave energy converter.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-179103 (URN)
Projects
The Lysekil Project
Available from: 2012-08-07 Created: 2012-08-07 Last updated: 2012-09-07
25. Using compactRIO for Control and Measurement in the Low Voltage Marine Substation at the LysekilWave Power Reseach Site
Open this publication in new window or tab >>Using compactRIO for Control and Measurement in the Low Voltage Marine Substation at the LysekilWave Power Reseach Site
2010 (English)Other (Refereed)
Place, publisher, year, pages
Austin, Texas, USA: National Instruments, 2010
Keyword
CompactRIO, Wave power, Control system, Graphical system design, achivement award.
National Category
Control Engineering
Identifiers
urn:nbn:se:uu:diva-179394 (URN)
Available from: 2012-08-14 Created: 2012-08-14 Last updated: 2012-09-07
26. The Lysekil Wave Power Project: Status Update
Open this publication in new window or tab >>The Lysekil Wave Power Project: Status Update
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2008 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97846 (URN)
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2014-04-29Bibliographically approved
27. Experimental results from an offshore wave energy converter
Open this publication in new window or tab >>Experimental results from an offshore wave energy converter
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2008 (English)In: Volume 6: Nick Newman Symposium on Marine Hydrodynamics; Yoshida and Maeda Special Symposium on Ocean Space Utilization; Special Symposium on Offshore Renewable Energy, 2008, 653-657 p.Conference paper, Published paper (Refereed)
Abstract [en]

Anoffshore wave energy converter (WEC) was successfully launched at theSwedish west coast in the middle of March 2006. TheWEC is based on a permanent magnet linear generator locatedon the ocean floor driven by a point absorber. Ameasuring station has been installed on a nearby island whereall measurements and experiments on the WEC have been carriedout. The output voltage from the generator fluctuates both inamplitude and frequency and must therefore be converted to enablegrid connection. In order to study the voltage conversion, themeasure station was fitted with a six pulse diode rectifierand a capacitive filter during the autumn of 2006. Theobject of this paper is to present a detailed descriptionof the existing wave energy system of the Islandsberg project.Special attention will be given to the power absorption bythe generator when it is connected to a non linearload

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-97845 (URN)10.1115/OMAE2008-57415 (DOI)
Conference
ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering (OMAE2008) June 15–20, 2008 , Estoril, Portugal
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2016-04-12Bibliographically approved
28. Temperature measurements in a linear generator and marine substation for wave power
Open this publication in new window or tab >>Temperature measurements in a linear generator and marine substation for wave power
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2010 (English)In: PROCEEDINGS OF THE ASME 29TH INTERNATIONAL CONFERENCE ON OCEAN,   OFFSHORE AND ARCTIC ENGINEERING 2010, VOL 3, 2010, 545-552 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper analyzes temperature measurements acquired in offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common DC-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. First results of temperature measurements on substation components and on the stator of one of the linear generators are presented from operation in linear and in non-linear damping. Results indicate that there might be some convective heat transport in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel to avoid heating from neighbouring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding PVC cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the WEC could be enhanced. Another suggested alteration would be to lower the resistive losses by reducing the linear generator current density.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-142500 (URN)000290556500066 ()978-0-7918-4911-8 (ISBN)
Conference
29th ASME International Conference on Ocean, Offshore and Arctic Engineering Shanghai, PEOPLES R CHINA, JUN 06-11, 2010 ASME, Ocean, Offshore, & Arctic Engn Div
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2016-04-18Bibliographically approved
29. A wave power unit
Open this publication in new window or tab >>A wave power unit
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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

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