uu.seUppsala University Publications
Change search
Refine search result
123456 1 - 50 of 255
CiteExportLink to result list
Permanent 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
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Apelfrojd, Senad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Back-to-Back 2L-3L Grid Integration of a Marine Current Energy Converter2015In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 2, p. 808-820Article in journal (Refereed)
    Abstract [en]

    The paper proposes a back-to-back 2L-3L grid connection topology for a marine current energy converter. A prototype marine current energy converter has been deployed by a research group at Uppsala University. The concept behind the prototype revolves around a fixed pitch vertical axis turbine directly connected to a permanent magnet synchronous generator (PMSG). The proposed grid connection system utilizes a well known and proven two level voltage source converter generator-side combined with a three-level cascaded H-bridge (CHB) multilevel converter grid-side. The multilevel converter brings benefits in terms of efficiency, power quality and DC-link utilization. The system is here presented for a single marine current energy converter but can easily be scaled up for clusters of marine current energy converters. Control schemes for both grid-side and generator-side voltage source converters are presented. The start-up, steady state and dynamic performance of the marine current energy converter are investigated and simulation results are presented in this paper.

  • 2.
    Apelfröjd, Senad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of Damping Strategies for Maximum Power Extraction from a Wave Energy Converter with a Linear Generator2014Conference paper (Refereed)
  • 3.
    Baránková, Hana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bárdos, Ladislav
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grabbe, Mårten
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Coatings for Renewable Energy: Paper JAPT-142009Conference paper (Refereed)
  • 4.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thermal Rating of a Submerged Substation for Wave Power2016In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 7, no 1, p. 436-445Article in journal (Refereed)
    Abstract [en]

    The costs of offshore maintenance operations put high reliability-requirements on offshore equipment for ocean energy, especially on submerged ones. Thermal management is thus essential in the design of the prototypes of a marine substation, developed at Uppsala University, for grid interface of wave power parks. The cooling system itself should be efficient as well as reliable. Therefore, the feasibility of a completely passive cooling strategy was evaluated. The studied substation includes various power components, which dissipate heat and are installed in one pressurized vessel. Thermal cross-coupling was investigated with 3-D submodels and a thermal network model. An electric circuit was coupled to determine the rated power of the substation. The results depend mainly on the dc-voltage, the seawater temperature, and the thermal contact between the components and the hull.

  • 5.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temperature Study in a Marine Substation for Wave Power2012In: International Journal of Mechanic Systems Engineering, ISSN 2225-7403, Vol. 2, no 4, p. 126-131Article in journal (Refereed)
  • 6.
    Bernhoff, Hans
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Leijon, Mats
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Conversion of wave energy to electricity2004In: Scandinavian Shipping Gazette, no October 1Article in journal (Other (popular scientific, debate etc.))
  • 7.
    Bernhoff, Hans
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabeth
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wave energy resources in sheltered sea areas: A case study of the Baltic Sea2006In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 31, no 13, p. 2164-2170Article in journal (Refereed)
    Abstract [en]

    Wave energy is a renewable source, which has not yet been exploited to a large extent. So far the main focus of wave energy conversion has been on the large wave energy resources of the great oceans on northern latitudes. However, large portions of the world potential wave energy resources are found in sheltered waters and calmer seas, which often exhibit a milder, but still steady wave climate. Examples are the Baltic Sea, the Mediterranean and the North Sea in Europe, and ocean areas closer to the equator. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. In the present work we instead focus on wave power plants consisting of a number of small wave energy converters, forming large arrays. In this context, we look at advantageous arrangements of point absorbers, and discuss the potential of the Baltic Sea as a case study.

  • 8.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Flywheel energy and power storage systems2007In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 11, no 2, p. 235-258Article in journal (Refereed)
    Abstract [en]

    For ages flywheels have been used to achieve smooth operation of machines. The early models where purely mechanical consisting of only a stone wheel attached to an axle. Nowadays flywheels are complex constructions where energy is stored mechanically and transferred to and from the flywheel by an integrated motor/generator. The stone wheel has been replaced by a steel or composite rotor and magnetic bearings have been introduced. Today flywheels are used as supplementary UPS storage at several industries world over. Future applications span a wide range including electric vehicles, intermediate storage for renewable energy generation and direct grid applications from power quality issues to offering an alternative to strengthening transmission. One of the key issues for viable flywheel construction is a high overall efficiency, hence a reduction of the total losses. By increasing the voltage, current losses are decreased and otherwise necessary transformer steps become redundant. So far flywheels over 10 kV have not been constructed, mainly due to isolation problems associated with high voltage, but also because of limitations in the power electronics. Recent progress in semi-conductor technology enables faster switching and lower costs. The predominant part of prior studies have been directed towards optimising mechanical issues whereas the electro technical part now seem to show great potential for improvement. An overview of flywheel technology and previous projects are presented and moreover a 200 kW flywheel using high voltage technology is simulated.

  • 9.
    Bolund, Björn
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Leijon, Mats
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Rotor configuration impact on generator ventilation needs2004In: IEEE PES Conference, New York, 2004Conference paper (Refereed)
  • 10.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Poynting theorem applied to cable wound generators2008In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, no 2, p. 600-605Article in journal (Refereed)
    Abstract [en]

    The use of cable windings in generators and transformers has a physical background which is hard to neglect. The work done by Maxwell, Poynting and Slepian combined with powerful finite element solver of today allows for visualization of electric and magnetic fields in different geometries. The electromagnetic fields and power flows for generator stator cables are in this article associated with Poynting's theorem. Geometrical design and insulation material properties are then linked to Poynting's theory showing that circular stator cables enable higher voltages while maintaining a high power flow. Today several high voltage generators and two transformers have been built and are currently in operation. This paper discusses the application of the Poynting Theorem to cable wound generators.

  • 11.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Segergren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Solum, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Perers, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lundström, Ludvig
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lindblom, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ericsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Nilsson, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ivanova, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Danielsson, O
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bengtsson, H
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, E
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Karlsson, K-E
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wolfbrandt, Ane
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rotating and Linear Syncronous Generators for Renewable Electric Energy Conversion: an Update of the Ongoing Research Projects at Uppsala University2004Conference paper (Other academic)
  • 12.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabeth
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Segergren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Upgrading Generators with new Tools and High Voltage Technology2004In: International journal on hydropower and dams, ISSN 1352-2523, Vol. 11, no 3, p. 104-108Article in journal (Refereed)
  • 13.
    Bostrom, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric resonance-rectifier circuit for renewable energy conversion2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 4, p. 043511-Article in journal (Refereed)
    Abstract [en]

    Variable speed generators are used more frequently for converting the energy from renewable energy sources to electric energy. The power production form a variable speed generator is dependent on the electrical damping of the generator. In this paper, a resonance circuit connected to a direct driven linear generator used for wave energy utilization is investigated. At resonance, the electrical damping in the generator increases which results in an increased power production. The results show that resonance can be achieved with the suggested circuit.

  • 14.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linear Generator Connected to a Resonance-Rectifier Circuit2013In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 38, no 2, p. 255-262Article in journal (Refereed)
    Abstract [en]

    This paper describes a linear direct driven generator used for wave energy utilization. The generator is placed on the seabed and connected to a buoy on the ocean surface. Due to the reciprocating motion of the translator, an electrical conversion system is needed between the wave energy converter (WEC) and the grid. Depending on how the conversion system is designed, the generator will be subjected to different loads. A novel conversion system is presented in this paper where the voltage from the WEC is rectified in a resonance circuit. Both simulations and experiments are performed on the circuit. The results from the simulations show that a higher power absorption and power production can be achieved with the resonance circuit compared to a WEC connected to a passive rectifier. A WEC, L9, developed by Uppsala University (Uppsala, Sweden) was used in the experiment. Significantly higher power absorption was obtained for L9 compared to power data from the first installed WEC, L1, at the Lysekil research site.

  • 15.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Operation analysis of a wave energy converter under different load conditions2011In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 5, no 3, p. 245-250Article in journal (Refereed)
    Abstract [en]

    This study analyses the electrical behaviour of a direct-driven linear generator under different load conditions. The studied generator is used in a wave energy converter (WEC) that converts the energy in ocean waves into electric energy. To enable a grid connection of a WEC, the voltage must be converted, and thereby, the generator will be subjected to a non-linear damping. Depending on how the conversion system is designed, the damping will be different. In the case studied, the voltage is first rectified, and on the dc-side of the rectifier the voltage is kept constant by controlling the power through a converter. In order to study the electrical behaviour of the generator in this operation mode, a simulation model was made in MATLAB Simulink. The model of the generator was verified with experimental data from an offshore operating WEC. The result of the study shows that the model of the generator agrees with the real generator and can be used for analysing the electrical behaviour of the WEC. Moreover, the results show that the operation with a non-linear load will be different compared to a linear load case.

  • 16.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stålberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thorburn, Karin
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental results of rectification and filtration from an offshore wave energy system2009In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 34, no 5, p. 1381-1387Article in journal (Refereed)
    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.

  • 17.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bolund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental results from an offshore wave energy converter2008In: Volume 6: Nick Newman Symposium on Marine Hydrodynamics; Yoshida and Maeda Special Symposium on Ocean Space Utilization; Special Symposium on Offshore Renewable Energy, 2008, p. 653-657Conference 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

  • 18.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bolund, Björn
    Eriksson, Mikael
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Results From an Offshore Wave Energy Converter2010In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 132, no 4, p. 041103-Article in journal (Refereed)
    Abstract [en]

    An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.

  • 19.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temperature measurements in a linear generator and marine substation for wave power2010In: PROCEEDINGS OF THE ASME 29TH INTERNATIONAL CONFERENCE ON OCEAN,   OFFSHORE AND ARCTIC ENGINEERING 2010, VOL 3, 2010, p. 545-552Conference 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.

  • 20.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temperature measurements in a linear generator and marine substation for wave power2012In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 134, no 2, p. 021901-Article in journal (Refereed)
    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.

  • 21.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gravråkmo, Halvar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Björklöf, Daniel
    Johansson, Tobias
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design proposal of electrical system for linear generator wave power plants2009In: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS, IEEE , 2009, p. 4180-4185Conference 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.

  • 22.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stålberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Study of aWave Energy Converter Connected to a Nonlinear Load2009In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 2, p. 123-127Article in journal (Refereed)
    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.

  • 23.
    Bouquerel, Mathias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fast aeroelastic model for straight bladed vertical axis wind and hydro turbines2010In: Wind Engineering, ISSN 0309-524XArticle in journal (Refereed)
  • 24.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper (Refereed)
    Abstract [en]

    Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

  • 25.
    Castellucci, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Markus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Apelfröjd, Senad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wireless System for Tidal Effect Compensation in the Lysekil Research Site2012In: Proceedings of the ASME 31st International Conference on Ocean, Offshore and Arctic Engineering, vol. 7, 2012, p. 293-298Conference paper (Refereed)
    Abstract [en]

    This paper describes, firstly, the rope adjustment device for wave energy converters (WECs) to minimize the tidal effect on the electricity production and, secondly, a wireless communication network between point absorbing WECs in the Lysekil Research Site and a computer station at the Department of Engineering Sciences at Uppsala University. The device is driven by a motor that activates when the main water level deviates from the average. The adjustment is achieved through a screw that moves upwards during low tides and downwards during high tides. For the purpose of testing the device in the research site, a wireless connection between the buoy in the sea and a computer on land will be designed. A sensor located close to the research site monitors the sea water level and, every time a significant variation is registered, it sends wirelessly a signal to the data logger that controls the power to the motor The position of the screw is observed by a second sensor and the measurements are retrieved back to Uppsala via GSM connection. The full scale device is tested in the lab and it is demonstrated to work properly, requiring less than 750 W to lift and lower different loads. Moreover, the wireless communication network is designed and once it will be built, it will allow to recall and store data, send information from one node of the system to another, monitor the proper functioning of the device and modify the control as desired.

  • 26.
    Castellucci, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Markus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tidal effect compensation system for point absorbing wave energy converters2013In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 51, p. 247-254Article in journal (Refereed)
    Abstract [en]

    Recent studies show that there is a correlation between water level and energy absorption values for the studied wave energy converters: the absorption decreases when the water levels deviate from average. The situation appears during tides when the water level changes significantly. The main objective of the paper is to present a first attempt to increase the energy absorption during tides by designing and realizing a small-scale model of a point absorber equipped with a device that is able to adjust the length of the rope connected to the generator. The adjustment is achieved by a screw that moves upwards in the presence of low tides and downwards in the presence of high tides. Numerical results as well as experimental tests suggest that the solution adopted to minimize the tidal effect on the power generation shows potential for further development.

  • 27.
    Chatzigiannakou, Maria A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore Deployment of Marine Substation in the Lysekil Research Site2015Conference paper (Refereed)
  • 28.
    Chatzigiannakou, Maria A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore Deployment of Point Absorbing Wave Energy Converters with a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, 2014Conference paper (Refereed)
    Abstract [en]

    Within the year 2013, four linear generators with point absorber buoy systems were deployed in the Lysekil test site. Until now, deployments of these point absorbing wave energy converters have been expensive, time consuming, complicated and raised safety issues. In the present paper, we focus on the analysis and optimization of the offshore deployment process of wave energy converters with a linear generator power take-off which has been constructed by Uppsala University. To address the crucial issues regarding the deployment difficulties, case study of previous offshore deployments at the Lysekil test site are presented regarding such parameters as safety, cost and time efficiency. It was discovered that the deployment process can be improved significantly, mainly by using new technologies, e.g., new specialized deployment vessels, underwater robots for inspections and for connecting cables and an automatized pressurizing process. Addressing the main deployment difficulties and constrains leads us to discovery of methods that makes offshore deployments more cost-efficient and faster, in a safety context.

  • 29.
    Chatzigiannakou, Maria Angiliki
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore Deployments of Wave Energy Converters by Seabased Industry AB2017In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 5, no 2, article id 15Article in journal (Refereed)
    Abstract [en]

    Since 2008, Seabased Industry AB (SIAB) has manufactured and deployed several units of wave energy converters (WECs) of different design. The WECs are linear generators with point absorber buoy systems that are placed on the seabed, mounted on a gravitation concrete foundation. These deployments have taken place in different areas, using different deployment vessels. Offshore deployments of WECs and underwater substations have so far been complicated procedures, that were both expensive and time-consuming. The focus of this paper is to discuss these deployments in terms of economy and time efficiency, as well as safety. Because seven vessels have been used to facilitate the deployments, an evaluation on the above basis is carried out for them. The main conclusions and certain solutions are presented for the various problems encountered during these deployments and the vessel choice is discussed. It is found that the offshore deployment process can be optimized in terms of cost, time efficiency and safety with a careful vessel choice, use of the latest available technologies and detailed planning and organizing.

  • 30.
    Chen, WenChuang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Tsinghua Univ, State Key Lab Hydrosci & Engn, Beijing 100084, Peoples R China..
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Zhang, YongLiang
    Tsinghua Univ, State Key Lab Hydrosci & Engn, Beijing 100084, Peoples R China..
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Numerical modelling of a point-absorbing wave energy converter in irregular and extreme waves2017In: Applied Ocean Research, ISSN 0141-1187, E-ISSN 1879-1549, Vol. 63, p. 90-105Article in journal (Refereed)
    Abstract [en]

    Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (WEC) with a stroke control system in irregular and extreme waves is presented. The model is validated by a comparison of the numerical results with the wave tank experiment results of other researchers. The validated model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in WEC’s performance exhibited by an inviscid fluid and a viscous fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height.

  • 31.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters2006In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 30, no 14, p. 1130-1145Article in journal (Refereed)
    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.

  • 32.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Flux Distribution in Linear Permanent-Magnet Synchronous Machines Including Longitudinal End Effects2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 7, p. 3197-3201Article in journal (Refereed)
    Abstract [en]

    We investigated the longitudinal ends' influence on the flux distribution in a permanent-magnet linear synchronous machine with an analytic model and with numeric finite-element methods. We derived a general analytic expression, on closed form, from a linear reluctance model. The model reveals that the flux in a linear machine differs from that in a rotating machine in several aspects. The longitudinal ends introduce a pairwise coupled flux pattern, which will behave differently in circuits with odd or even numbers of magnets. In linear machines with an even number of magnets the pairwise coupled flux will spread throughout the whole machine, whereas in linear machines with an odd number of magnets it will be transformed into an equally distributed flux in the middle. The latter case will give rise to a nonsymmetric air gap flux distribution, where every second pole has larger flux. We confirmed the pairwise coupled flux and the nonsymmetric air gap distribution predicted by the analytic model by finite-element simulations. We noted additional effects when nonlinear behavior of the steel is taken into account. We conclude that saturation counteracts the pairwise coupled flux pattern at the longitudinal ends. Again, a nonsymmetric air gap flux distribution occurs as the pairwise coupled flux is transformed into an equally coupled flux. The pairwise coupling of the flux and the nonsymmetric air gap flux distribution give rise to a number of secondary effects, which we discuss.

  • 33.
    Danielsson, Oskar
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Leijon, Mats
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Sjöstedt, Elisabeth
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator2005In: IEEE Transactions on Magnetics, Vol. 41, no 9, p. 2490-2495Article in journal (Refereed)
  • 34.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjöstedt, Elisabeth
    Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator2006In: IEEE Transactions on Magnetics, Vol. 41, no 9, p. 2490-2495Article in journal (Refereed)
  • 35.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    A direct drive wave energy converter: Simulations and experiments2005In: Proc of 24th International Conference on Offshore Mechanics & Arctic Engineering, American Society of Mechanical Engineers , 2005Conference paper (Refereed)
  • 36.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabeth
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Simulated Response of a Linear Generator Wave Energy Converter2004In: Proceedings of the Fourteenth International Offshore and Polar Engineering Conference, 2004, p. 260-260Conference paper (Refereed)
  • 37.
    Danielsson, Oskar
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Thorburn, Karin
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Eriksson, Mikael
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Leijon, Mats
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Permanent magnet fixation concepts for linear generator2003In: Fifth European Wave Energy Conference 17-19 Sept., 2003Conference paper (Refereed)
  • 38.
    David, Österberg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Multi-Body Vortex Method Applied to Vertical Axis Wind Turbines2010Article in journal (Refereed)
  • 39.
    de Santiago, Juan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ferhatovic, Senad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electrical Motor Drivelines in Commercial All Electric Vehicles: a Review2012In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 61, no 2, p. 475-484Article in journal (Refereed)
    Abstract [en]

    This paper presents a critical review of the drivelines in all Electric Vehicles (EVs). The motor topologies that are the best candidates to be used in EVs are presented. The advantages and disadvantages of each electric motor type are discussed from a system perspective. A survey of the electric motors used in commercial EVs is presented. The survey shows that car manufacturers are very conservative when it comes to introducing new technologies. Most of the EV’s in the market mount a single induction or permanent magnet motor with a traditional mechanic driveline with a differential. The study illustrates that comparisons between the different motors are made difficult by the large number of parameters and the lack of a recommended test scheme. The authors propose that a standardized drive cycle is used to test and compare motors.

  • 40.
    Deglaire, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Conformal mapping and efficient boundary element method without, boundary elements for fast vortex particle simulations2008In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 27, no 2, p. 150-176Article in journal (Refereed)
    Abstract [en]

    In this paper, a revitalization of conformal mapping methods applied to fluid flows in two dimensions is proposed. The present work addresses several important issues concerning their application for vortex particle flow solvers. Difficulties of past conformal based method are reviewed. One difficulty concerns the ability of a mapping procedure to represent complicated shapes. The present paper improves past algorithms to be able to map new shapes, including multiply connected domains. A new fast procedure allows transferring a set of points in the mapped simplified plane to the complicated domain and vice versa. After a mapping construction, it is demonstrated how basic exact solutions to potential flow problems with vortices can be put in a new form which provides a faster and more accurate computation than with distributed singularity methods.

  • 41.
    Dolguntseva, Irina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Seabased Industry AB.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Risk based estimation of failure in a steel wire used for the wave energy converter connection line2014Conference paper (Refereed)
    Abstract [en]

    The wave energy converter being developed at Uppsala University is of a point absorber type utilizing heaving motion of waves with a direct driven linear generator power take off. The point absorber, a buoy, is placed on the sea surface and is connected to the translator by a connection line. The connection line service life is of large importance for the lifetime of the entire device. Steel wire used as the connection line should be chosen to withstand loadings with different amplitude and frequency. In the present study, the risk of failure in the connection line is estimated.

  • 42.
    Dolguntseva, Irina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Krishna, Remya
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Elamalayil Soman, Deepak
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Contour-Based Dead-Time Harmonic Analysis in a Three-Level Neutral-Point-Clamped Inverter2015In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 62, no 1, p. 203-210Article in journal (Refereed)
    Abstract [en]

    The term dead time refers to a prime safety factor for most power electronic converter topologies, and it is included either in the control software or in the gate/base driver hardware, depending on the application as well as the control requirements. In this paper, the authors present a comprehensive numerical analysis of dead-time effects on the output voltage of a three-level neutral-pointclamped (NPC) inverter. To incorporate the dead-time effect in the output voltage, 3-D models of three-level carrier pulse width modulation (PWM) methods are modified for two dead-time implementations. Closed-form expressions of inverter phase voltage harmonics for phase opposition disposition (POD) PWM are derived based on the double Fourier series approach and modified contour plots. The harmonic spectra from numerical evaluations, simulations, and experiments for natural sampling (NS), symmetrical regular sampling (SRS), and asymmetrical regular sampling (ARS) are compared to validate the mathematical models. In addition, the fundamental voltage with respect to the dead time and the load phase angle is presented based on analytical results and simulation.

  • 43.
    Dolguntseva, Irina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nguyen, Minh-Thao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance enhancement of a vertical axis cross-flow hydro-kinetic energy converter2014Conference paper (Other academic)
  • 44.
    Ekergård, Boel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hagnestål, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental results from a linear wave power generator connected to a resonance circuit2012In: Wiley Interdisciplinary Reviews: Energy and Environment, ISSN 2041-8396, E-ISSN 2041-840X, Vol. 2, no 4, p. 456-464Article in journal (Refereed)
    Abstract [en]

    The output voltage from a direct-driven permanent magnet linear generator installed in a wave power plant varies both in amplitude and frequency. Electrical conversion is therefore necessary before grid connection can be achieved. The aim of this paper is to present an electrical conversion system based on the electric resonance phenomena. As one of the first steps in the development, and to gain further knowledge and understanding of the proposed resonance circuit, experimental tests with a single-phase permanent magnet linear generator connected to a resonance circuit were performed. The experimental results presented in this paper indicated that a successful resonance between the generator and external circuit was achieved. The research regarding the wave energy converters lies within The Lysekil Wave Power Project at Uppsala University and has been ongoing since 2002.

  • 45.
    Ekergård, Boel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Axial Force Damper in a Linear Wave Energy Converter2013In: Development and Applications of Oceanic Engineering (DAOE), ISSN 2325-3762, Vol. 2, no 2, p. 33-38Article in journal (Refereed)
    Abstract [en]

    This paper presents a study on the axial force damper in a wave energy converter. The converter itself consists of a linear generator placed on the ocean floor connected to a buoy at the ocean surface. As the development of the complete system goes forward, the economical perspective becomes more and more important. In order to ensure an economically viable alternative to the electric energy conversion, the costs associated with the use of materials have to be reduced while the survivability of the wave power unit has to be prolonged. The study presented in this paper increases the knowledge on axial forces and illustrates the damping system required to prevent the failure of the hull which houses the generator. The results are aimed to be utilized in the future design of wave energy converters and influence the choice of materials, the total costs and prolong the survivability of the wave energy converters in harsh wave climates.

  • 46.
    Ekergård, Boel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gravråkmo, Halvar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Theory and Simulations of an End Stop Solution in a Linear Wave Power GeneratorManuscript (preprint) (Other academic)
  • 47.
    Ekergård, Boel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ideal Analytical Expression of the Magnetic Circuit in a Permanent Magnet Linear Machine2013In: Proceedings of the Ecological Vehicles and Renewable Energies (EVER), 2013, 2013, p. 1-6Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to presents a study and derived expressions of the magnetic flux density in the air-gap of the linear synchronous permanent magnet generator, utilized in the wave energy converter. The significance of a well-modelled magnetic flux density-term is important, when, for example, modelling the induced voltage and dimension the support structure due to the magnetic force between the stator and translator at no load situation.

  • 48.
    Ekergård, Boel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Prediction of the Inductance in a Synchronous Linear Permanent Magnet Generator2011In: Journal of Electromagnetic Analysis and Applications, ISSN 1942-0730, E-ISSN 1942-0749, Vol. 3, no 5, p. 155-159Article in journal (Refereed)
    Abstract [en]

    This paper presents calculations of the varying inductances profile for a synchronous linear surface mounted permanent magnet generator in an ABC reference system. Calculations are performed by utilizing the reluctance term, known from analytic calculations and finite element method simulations. With the inductance term identified, the voltage difference between the generator’s no load and load voltage can be calculated and an external circuit can be designed for optimal use of the generator. Two different operation intervals of the linear generator are considered and the results are discussed. The result indicates that time costly finite element simulations can be replaced with simple analytical calculations for a surface mounted permanent magnet linear generator.

  • 49.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjökvist, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mats, Leijon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Complete Design of a Rare Earth Metal-Free Permanent Magnet Generator2014In: Machines, ISSN 2075-1702Article in journal (Refereed)
    Abstract [en]

    The price of rare-earth metals used in neodymium-iron-boron (NdFeB) permanent magnets (PMs) has fluctuated greatly recently. Replacing the NdFeB PMs with more abundant ferrite PMs will avoid the cost insecurity and insecurity of supply. Ferrite PMs have lower performance than NdFeB PMs and for similar performance more PM material has to be used, requiring more support structure. Flux concentration is also necessary, for example, by a spoke-type rotor. In this paper the rotor of a 12 kW NdFeB PM generator was redesigned to use ferrite PMs, reusing the existing stator and experimental setup. Finite element simulations were used to calculate both electromagnetic and mechanical properties of the design. Focus was on mechanical design and feasibility of construction. The result was a design of a ferrite PM rotor to be used with the old stator with some small changes to the generator support structure. The new generator has the same output power at a slightly lower voltage level. It was concluded that it is possible to use the same stator with either a NdFeB PM rotor or a ferrite PM rotor. A ferrite PM generator might require a larger diameter than a NdFeB generator to generate the same voltage.

  • 50.
    Ekström, Rickard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Apelfröjd, Senad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Verifications of Offshore Marine Substation for Grid-Connection of Wave Energy Farm2013Conference paper (Refereed)
123456 1 - 50 of 255
CiteExportLink to result list
Permanent 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