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Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
2006 (English)In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 30, no 14, 1130-1145 p.Article 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.

Place, publisher, year, edition, pages
2006. Vol. 30, no 14, 1130-1145 p.
Keyword [en]
design methodology, finite element, linear synchronous generators, permanent magnet, wave energy converter
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-95676DOI: 10.1002/er.1209ISI: 000242188900002OAI: oai:DiVA.org:uu-95676DiVA: diva2:169985
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Modelling and Experimental Verification of Direct Drive Wave Energy Conversion: Buoy-Generator Dynamics
Open this publication in new window or tab >>Modelling and Experimental Verification of Direct Drive Wave Energy Conversion: Buoy-Generator Dynamics
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on development of models and modelling of a wave energy converter in operation. Through the thesis linear potential wave theory has been used to describe the wave-buoy interaction. The differences lie in the generator models, in the simplest model the generator is a mechanical damper characterized by a damping factor. In the most advanced generator model the magnetic fields is calculated the by a FE-method, which gives detailed description of the electric properties and the effect it has on the buoy dynamics. Moreover, an equivalent circuit description of the generator has been tested. It has the same accuracy as the field based model but with a strongly enhanced CPU time. All models are verified against full scale experiments. The models are intended to be used for design of the next generation wave energy converters. Further, the developed models have also been used to study what effect buoy geometry and generator damping have on the ability to energy absorption.

In the spring 2006 a full scale wave energy converter was installed at the west coast of Sweden. It was in operation and collected data during three months. During that period the load resistance was varied in order to study the effect on the energy absorption. These collected data was then used in the verification of the developed models.

In the year 2002 a wave energy project started at Uppsala University; this work is a part of that larger project which intendeds to develop a viable wave energy conversion concept.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 287
Keyword
Engineering physics, Wave energy, Potential wave theory, Linear generator, Simulations, Experiments, Point absorber, FEM, Equivalent circuit theory, Teknisk fysik
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-7785 (URN)978-91-554-6850-7 (ISBN)
Public defence
2007-04-13, Polhemsalen, Ångströmlaboratoriet, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2010-11-10Bibliographically approved
2. Wave Energy Conversion: Linear Synchronous Permanent Magnet Generator
Open this publication in new window or tab >>Wave Energy Conversion: Linear Synchronous Permanent Magnet Generator
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. 102 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 232
Keyword
Engineering physics, Finite element method, linear synchronous generator, longitudinal end effect, permanent magnet, point absorber, offshore testing, wave power, Teknisk fysik
Identifiers
urn:nbn:se:uu:diva-7194 (URN)91-554-6683-4 (ISBN)
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

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Danielsson, OskarEriksson, MikaelLeijon, Mats

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