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Wave Energy Conversion: Linear Synchronous Permanent Magnet Generator
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies the electric aspects of a linear synchronous permanent magnet generator. The generator is designed for use in a wave energy converter, which determines the fundamental requirements of the generator. The electromagnetic properties of the generator are investigated with a finite element based simulation tool. These simulations formed the base of the design and construction of a laboratory prototype. Several experiments where conducted on the prototype generator. The results verify at large the simulation tool. However, a difference between the measured and simulated air gap flux was discovered. This was attributed to the longitudinal ends of the generator, which are ignored in the simulation tool. Experiences from the construction, and further finite element studies, led to a significant change in the support structure of the first offshore prototype generator. A complete wave energy converter was constructed and launched, the 13th of March, on the west coast of Sweden. A study of the load resistance impact on the power absorption has been carried out. An optimal load interval, with regard to power absorption, has been identified. Furthermore, the generator has proofed to withstand short term overload several times larger than the nominal load. Finally, the longitudinal ends’ influence on the flux distribution was investigated with an analytical model, as well as finite element simulations. A possible problem with large induction of eddy currents in the actuator back steel was identified.

This work is a part of a larger project, which aims do develop a viable wave energy conversion system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2006. , p. 102
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 232
Keywords [en]
Engineering physics, Finite element method, linear synchronous generator, longitudinal end effect, permanent magnet, point absorber, offshore testing, wave power
Keywords [sv]
Teknisk fysik
Identifiers
URN: urn:nbn:se:uu:diva-7194ISBN: 91-554-6683-4 (print)OAI: oai:DiVA.org:uu-7194DiVA, id: diva2:169037
Public defence
2006-11-10, Siegbahnsalen, Ångströmlaboratoriet, Box 534, Uppsala, 13:15
Opponent
Supervisors
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2013-07-26Bibliographically approved
List of papers
1. Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator
Open this publication in new window or tab >>Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator
2006 (English)In: IEEE Transactions on Magnetics, Vol. 41, no 9, p. 2490-2495Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-94984 (URN)
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2018-05-31Bibliographically approved
2. Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters
Open this publication in new window or tab >>Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters
2006 (English)In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 30, no 14, p. 1130-1145Article in journal (Refereed) Published
Abstract [en]

A directly coupled linear permanent magnet generator of longitudinal flux-type is investigated. The generator will be used for power take-off in a wave energy converter. A combined field- and circuit model, solved by a time stepping finite element technique, is used to model and analyse the electromagnetic behaviour of the machine. A large number of simulations form the basis of a design study where the influence of armature current level, number of cables per slot, and pole width is investigated with respect to efficiency, generator size, and the load angle. A case study is performed for a chosen generator design. The electromagnetic behaviour is examined both for nominal load and for overloads. The generator has a nominal output power of 10 kW for a constant piston speed of 0.7 m s(-1). The electromagnetic efficiency at nominal load is 86.0%, the load angle 6.6 degrees, and the power fluctuation 1.3%. At 300% overload the load angle barely exceeds 12 degrees and the cable temperature is below 25 degrees C provided that the stator back is thermally connected to the sea water. The numerical calculations have been verified for small speeds by experiments.

Keywords
design methodology, finite element, linear synchronous generators, permanent magnet, wave energy converter
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-95676 (URN)10.1002/er.1209 (DOI)000242188900002 ()
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
3. Verification of Cyclic Boundary Condition and 2D Field Model for Synchronous PM Linear Generator
Open this publication in new window or tab >>Verification of Cyclic Boundary Condition and 2D Field Model for Synchronous PM Linear Generator
In: IEEE Transaction on MagneticsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-94986 (URN)
Available from: 2006-10-20 Created: 2006-10-20Bibliographically approved
4. First experimental results from sea trials of a novel wave energy system
Open this publication in new window or tab >>First experimental results from sea trials of a novel wave energy system
Show others...
In: Applied Physics LetterArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-94987 (URN)
Available from: 2006-10-20 Created: 2006-10-20Bibliographically approved
5. Analytic model of flux distribution in linear PM synchronous machines including longitudinal end effects
Open this publication in new window or tab >>Analytic model of flux distribution in linear PM synchronous machines including longitudinal end effects
In: Submitted to IEEE Transaction on MagneticsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-94988 (URN)
Available from: 2006-10-20 Created: 2006-10-20Bibliographically approved
6. Electromagnetic forces in the air gap of a permanent magnet linear generator at no load
Open this publication in new window or tab >>Electromagnetic forces in the air gap of a permanent magnet linear generator at no load
2006 (English)In: Journal of Applied Physics, Vol. 99, no 3, p. 1-5Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-94989 (URN)
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2016-06-22Bibliographically approved
7. Measuring air gap width of permanent magnet linear generators using search coil sensor
Open this publication in new window or tab >>Measuring air gap width of permanent magnet linear generators using search coil sensor
2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 2, p. 024518-Article in journal (Refereed) Published
Abstract [en]

A concept for a wave power plant is being developed at the Centre for Renewable Electric Energy Conversion at the A˚ngström Laboratory at Uppsala University. The concept is based on a permanent magnet linear generator placed on the seabed, directly driven by a surface following buoy. Critical for the survival of the generator is that the air gap between the moving and static parts of the generator is constantly fixed at the designed width to prevent the moving and static parts from connecting during operation. This paper shows the design and evaluation of an inductive sensor for measuring the air gap width during generator operation. In order to survive during years on the seafloor inside the wave power plants, the sensor has deliberately been chosen to be a passive component, as well as robust and compact. A coil etched on a printed circuit board, i.e., a search coil, was the chosen basis for the sensor. The sensor has been tested on an existing test rig of a wave power plant and the results have been compared with finite element simulations.The results show that a search coil magnetic sensor etched on a printed circuit board is a suitable concept for measuring the air gap width. Experimentally measured and theoretically calculated sensor signals show very good agreement. The setup has a sensitivity of +/-0.4 mm in the range of 4-9.5 mm air gap. The potential for future improvements of the sensitivity is considerable.

Keywords
High-current and high-voltage technology: power systems; power transmission lines and cables, Electric motors, Spatial dimensions, Sensors ; remote sensing, Finite-element and Galerkin methods
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-94990 (URN)10.1063/1.2403964 (DOI)000243890800148 ()
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2017-12-14Bibliographically approved
8. An electrical approach to wave energy conversion
Open this publication in new window or tab >>An electrical approach to wave energy conversion
Show others...
2006 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, no 31, p. 1309-1319Article in journal (Refereed) Published
Abstract [en]

Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric power conversion of the vast ocean wave energy. The suggested linear electric energy converter is adapted to the natural wave motion using straightforward technology. Extensive simulations of the wave energy concept are presented, along with results from the experimental setup of a multisided permanent magnet linear generator. The prototype is designed through systematic electromagnetic field calculations. The experimental results are used for the verification of measurements in the design process of future full-scale direct wave energy converters. The present paper, describes the energy conversion concept from a system perspective, and also discusses the economical and some environmental considerations for the project.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-95677 (URN)10.1016/j.renene.2005.07.009 (DOI)
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
9. Simulated Response of a Linear Generator Wave Energy Converter
Open this publication in new window or tab >>Simulated Response of a Linear Generator Wave Energy Converter
2004 (English)In: Proceedings of the Fourteenth International Offshore and Polar Engineering Conference, 2004, p. 260-260Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-94992 (URN)1-880633-62-1 (ISBN)1098-6189 (ISBN)
Conference
ISOPE, 23-28 May, 2004, Toulon, France
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2013-07-31Bibliographically approved
10. A direct drive wave energy converter: Simulations and experiments
Open this publication in new window or tab >>A direct drive wave energy converter: Simulations and experiments
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2005 (English)In: Proc of 24th International Conference on Offshore Mechanics & Arctic Engineering, American Society of Mechanical Engineers , 2005Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
American Society of Mechanical Engineers, 2005
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-94993 (URN)
Conference
24th International Conference on Mechanics and Arctic Engineering (OMAE), Halkidiki, Greece, June 12-17
Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2013-07-31Bibliographically approved

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