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An electrical approach to wave energy conversion
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
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2006 (English)In: Renewable energy, ISSN 0960-1481, no 31, 1309-1319 p.Article 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.

Place, publisher, year, edition, pages
2006. no 31, 1309-1319 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-95677DOI: 10.1016/j.renene.2005.07.009OAI: oai:DiVA.org:uu-95677DiVA: diva2:169986
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-01-25Bibliographically 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. Electric Energy Conversion Systems: Wave Energy and Hydropower
Open this publication in new window or tab >>Electric Energy Conversion Systems: Wave Energy and Hydropower
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electric energy conversion is an important issue in today's society as our daily lives largely depend on the supplies of energy. Two energy sources are studied for conversion in the present thesis, ocean waves and hydropower. The work focuses on the generator and the transmission of its output to the electric grid.

Different approaches have been used, over the years, to convert the energy in ocean waves, and the method presently used is based on a point absorber (buoy) directly coupled to a linear generator on the seabed. A varying alternating voltage is induced with such configuration, where both the amplitude and the frequency changes continuously. The target is to connect several units in a farm, and thereby decrease the fluctuations in power production. This is shown to be possible to accomplish with a rectifier connected to each generator. Transmission systems can be designed with converters and transformers to connect the farm to the electric grid onshore. Several aspects of the concept are considered as well as interconnection issues. Analytical calculations verified by finite element simulations and measured data are used to model the behaviour of a linear generator. A series expanded expression for the ideal no-load flux and EMF (electromotive force) is derived, which can be developed into an analytical transmission design tool.

Hydropower has been used for more than a century. Today many of the stations from the mid 1900's are up for refurbishment. Studies with finite element calculations show that a higher electric efficiency can be obtained with a high voltage cable wound generator.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 202
Keyword
Engineering physics, Ocean wave power, renewable energy, linear generator, farm simulation, Teknisk fysik
Identifiers
urn:nbn:se:uu:diva-7081 (URN)91-554-6617-6 (ISBN)
Public defence
2006-09-22, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15
Opponent
Supervisors
Available from: 2006-09-01 Created: 2006-09-01 Last updated: 2013-07-31Bibliographically approved
3. 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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Leijon, MatsBernhoff, HansIsberg, JanSundberg, JanÅgren, OlovWolfbrandt, Arne

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