Change search
Refine search result
3456789 251 - 300 of 1771
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • 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.
  • 251.
    Bolund, BF
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Berglund, M
    Bernhoff, H
    Dielectric study of water/methanol mixtures for use in pulsed-power water capacitors2003In: Journal of Applied Physics, Vol. 93, no 5, p. 2895-2899Article in journal (Refereed)
  • 252.
    Bolund, Björn
    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.
    High Voltage Generators for Generation and Storage of Electric Energy2004Licentiate thesis, monograph (Other scientific)
  • 253.
    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.

  • 254.
    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)
  • 255.
    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.

  • 256. Bormann, Dierk
    et al.
    Midya, Surajit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    DC Components in Pantograph Arcing: Mechanisms and Influence of Various Parameters2007Conference paper (Refereed)
  • 257.
    Borsche, Theodor S.
    et al.
    Swiss Fed Inst Technol, Dept Elect Engn & Informat, Power Syst Lab, CH-8092 Zurich, Switzerland.
    de Santiago, Juan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Andersson, Göran
    Swiss Fed Inst Technol, Dept Elect Engn & Informat, Power Syst Lab, CH-8092 Zurich, Switzerland.
    Stochastic control of cooling appliances under disturbances for primary frequency reserves2016In: Sustainable Energy, Grids and Networks, ISSN 0284-4354, E-ISSN 2352-4677, Vol. 7, p. 70-79Article in journal (Refereed)
    Abstract [en]

    To stabilize power system frequency both in normal operation and after a contingency, a hierarchy of distributed-proportional and centralized-integral controllers is employed in most power systems. Providing proportional control–commonly referred to as primary frequency control or droop–with conventional generators constitutes significant cost. This led to strong interest in utilizing demand response as a cost-effective primary control reserve. This paper investigates an approach that allows a population of domestic refrigerators to reliably and continuously adjust its demand proportional to system frequency. The control relies exclusively on stochastic switching of refrigerators, and thus avoids synchronization and implementation issues associated with control strategies based on temperature-band adjustments. The scheme is tested on a realistic two-area power system model to investigate interaction with system frequency. The modeling of refrigerators is refined by analyzing the effect of door openings on cooling demand, and response of the refrigerator population under these conditions is described both analytically and with simulations.

  • 258.
    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.

  • 259.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electrical System of a Wave Power Plant2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several techniques to convert the energy in the ocean waves into electric energy. The wave energy converter presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. By keeping the generator as simple as possible and minimizing the number of mechanical parts, the lifetime of the generator is believed to increase. To convert and interconnect the power from the generators, marine substations are used. The marine substation will be placed on the seabed and it will convert the AC with variable amplitude and variable frequency from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the conversion, the rectification and filtering. The purpose with the study was to investigate how the generator will operate when it is connected to a non-linear load and to obtain guidelines on how larger systems could be designed. Another aim with the experiment was to see to which extent the voltage and power out from the generator can be smoothened. Offshore experiments and simulations have been done on a full scale generator connected to a diode rectifier and filter. The results show that a smooth DC output voltage after the rectifier has small ripple content. The kind of load and value of load will have an impact on the generators ability to absorb and produce power. The highest amount of absorbed power is achieved at the highest damping of the system. However, the highest damping function does not necessarily coincide with the maximum produced power. In connection to the installation of two new wave energy converters on the Swedish west coast, a marine substation will be launched at the site. Laboratory tests have been done on the marine substation and it worked as expected and the experimental data had a good agreement with the simulated data.

  • 260.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electrical Systems for Wave Energy Conversion2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several technologies on how to convert the energy in the ocean waves into electric energy. The wave energy converter (WEC) presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power.

    To convert and interconnect the power from the generators, marine substations are used. The marine substations are placed on the seabed and convert the fluctuating AC from the generators into an AC suitable for grid connection.

    The work presented in the thesis focuses on the first steps in the electric energy conversion, converting the voltage out from the generators into DC, which have an impact on the WEC's ability to absorb and produce power. The purpose has been to investigate how the generator will operate when it is subjected to different load cases and to obtain guidelines on how future systems could be improved. Offshore experiments and simulations have been done on full scale generators connected to four different loads, i.e. one linear resistive load and three different non-linear loads representing different cases for grid connected WECs.

    The results show that the power can be controlled and optimized by choosing a suitable system for the WEC. It is not obvious which kind of system is the most preferable, since there are many different parameters that have an impact on the system performance, such as the size of the buoy, how the generator is designed, the number of WECs, the highest allowed complexity of the system, costs and so on. Therefore, the design of the electrical system should preferably be carried out in parallel with the design of the WEC in order to achieve an efficient system.

  • 261.
    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.
    Eriksson, Mikael
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linear generator connected to a resonance circuitIn: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed)
  • 262.
    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.

  • 263.
    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.

  • 264.
    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.

  • 265.
    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

  • 266.
    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.

  • 267.
    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.

  • 268.
    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.

  • 269.
    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.

  • 270.
    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.

  • 271.
    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)
  • 272. Bourikas, Leonidas
    et al.
    Shen, Tianfeng
    James, P.A.B.
    Chow, David
    Jentsch, Mark F.
    Darkwa, J.
    Bahaj, A. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Addressing the challenge of interpreting microclimatic weather data collected from urban sites2013In: Journal of Energy and Power Engineering, ISSN 1934-8975, E-ISSN 1934-8983, Journal of Power and Energy Engineering, Vol. 1, no 5, p. 7-15Article in journal (Refereed)
    Abstract [en]

    This paper presents some installation and data analysis issues from an ongoing urban air temperature and humidity measurement campaign in Hangzhou and Ningbo, China. The location of the measurement sites, the positioning of the sensors and the harsh conditions in an urban environment can result in missing values and observations that are unre-presentative of the local urban microclimate. Missing data and erroneous values in micro-scale weather time series can produce bias in the data analysis, false correlations and wrong conclusions when deriving the specific local weather patterns. A methodology is presented for the identification of values that could be false and for determining whether these are “noise”. Seven statistical methods were evaluated in their performance for replacing missing and erroneous values in urban weather time series. The two methods that proposed replacement with the mean values from sensors in locations with a Sky View Factor similar to that of the target sensor and the sensors closest to the target’s location per-formed well for all Day-Night and Cold-Warm days scenarios. However, during night time in warm weather the re-placement with the mean values for air temperature of the nearest locations outperformed all other methods. The results give some initial evidence of the distinctive urban microclimate development in time and space under different regional weather forcings.

  • 273.
    Bozzi, S.
    et al.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Bizzozero, F.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Gruosso, G.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Passoni, G.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analysis of Interaction of Point Absorbers' Arrays for Seawave Electrical Energy Generation in Italian Seas2016In: 2016 International Symposium On Power Electronics, Electrical Drives, Automation And Motion (SPEEDAM), 2016, p. 1369-1374Conference paper (Refereed)
    Abstract [en]

    This work focuses on interactions between wave energy converters (WEC) in array configuration. The arrays are simulated in the time domain by a coupled hydrodynamic electromagnetic model. The hydrodynamic parameters of the model are estimated by boundary element code while the electrical ones are obtained by finite element code. Wave parks of two and four devices are simulated considering different layouts. The ultimate goal of the work is to identify the optimal array design at four Italian locations. The results show that: (i) it is possible to find an array configuration which performs better than four isolated devices, at each study sites, (ii) the highest energy production is obtained with the linear layout at all the locations, (ii) optimum WEC distance varies between ten and twenty diameters, depending on the deployment site and (iv) the difference in energy production between the best and worst array configuration (i.e. over all the possible combinations of geometrical layout, spatial orientation and WEC distance) ranges from 3% to 7%, depending on the deployment site..

  • 274.
    Bozzi, Silvia
    et al.
    Politecn Milan, Dept Elect Informat Sci & Bioengn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Miguel, Adria Moreno
    Univ Bologna, Dept Civil Environm & Mat Engn, Viale Risorgimento 2, I-40136 Bologna, Italy..
    Antonini, Alessandro
    Univ Plymouth, Coastal Ocean & Sediment Transport Res Grp, Marine Bldg, Plymouth PL4 8AA, Devon, England..
    Bizzozero, Federica
    Politecn Milan, Dept Elect Informat Sci & Bioengn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Gruosso, Giambattista
    Politecn Milan, Dept Elect Informat Sci & Bioengn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Archetti, Renata
    Univ Bologna, Dept Civil Environm & Mat Engn, Viale Risorgimento 2, I-40136 Bologna, Italy..
    Passoni, Giuseppe
    Politecn Milan, Dept Elect Informat Sci & Bioengn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Wave energy farm design in real wave climates: the Italian offshore2017In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 122, p. 378-389Article in journal (Refereed)
    Abstract [en]

    The work focuses on hydrodynamic interactions between heaving wave energy converters (WEC). Wave parks of four devices are simulated in the time domain by a hydrodynamic-electromagnetic model, coupled with a boundary element code for the estimation of hydrodynamic parameters. Different layouts (linear, square and rhombus), WEC separation distances (5, 10, 20 and 30 buoy diameters) and incident wave directions (30 degrees apart) are considered to assess the effect of design parameters on array power production. Then, a site-specific design optimization is carried out for different Italian locations and some key insights on wave farm design in real wave climates are provided. The results show that the effect of wave interactions on energy absorption is not expected to be a main issue, as long as the devices are separated by at least 10 buoy diameters and that the layouts are oriented to achieve the maximum energy absorption for the prevailing wave direction.

  • 275. Brandenburg, Ronny
    et al.
    Baránková, Hana
    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.
    Plasma-based depollution of exhausts: principles, state of the art and future prospects2011In: Monitoring, Control and Effects of Air Pollution / [ed] Andrzej G. Chmielewski, InTech , 2011Chapter in book (Refereed)
  • 276.
    Bränd, Emelie
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Olofsson, Ann-Mari
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experiments and simulations of the flow velocity distribution downstream the Xiluodu hydropower station2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Hydropower is a more environmental friendly way of producing electric power than many other alternatives today. Though, the effects of constructing mega dams are much tangible for the local eco systems in addition to changing many people’s lives forever. In order to prevent floods, riverbank erosions or landslides, proper investigations of the environmental impact from dam constructions must be performed. One of the key parameters in such investigations is the flow discharge velocity.

    This master thesis treats experimental measurements and numerical simulations of the velocity downstream a model of Xiluodu dam. The Xiluodu dam is a mega dam under construction in China and will have a total capacity of 12 600 MW when completed. The model is in scale 1:100 and the experiments have been performed at Department of Hydraulic Engineering, Tsinghua University, Beijing, China.

    The velocity profile shows that the velocity in the middle of the river is larger than the velocity at the surface and near the riverbank. The comparison between the measured and the simulated velocities shows a difference of less than 20 percent in almost all points which can be considered as a good result. In those points where the difference is more than 20 percent, this is believed to be due to the position of these points. Some of them were located near a vortex and others very close to the bottom. This is a problem when sparsely measured topography in combination with linear interpolation makes the boundaries of the simulations incorrect.

    In order to perform better simulations, more densely topography data and better flow boundary conditions should be used. More measuring points of the velocity could also improve the result.

  • 277.
    Butorin, Sergei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kvashnina, K. O.
    European Synchrotron, Grenoble, France; HZDR, Inst Resource Dresden, Germany.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kavcic, M.
    Joief Stefan Inst, Ljubljana, Slovenia.
    Zitnik, Mihael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Joief Stefan Inst, Ljubljana, Slovenia; Univ Ljubljana, Fac Math & Phys, Ljubljana, Slovenia.
    Bucar, K.
    Joief Stefan Inst, Ljubljana, Slovenia.
    Gougeon, P.
    Univ Rennes 1, INSA Rennes, Inst Sci Chim Rennes, Rennes, France.
    Gall, P.
    Univ Rennes 1, INSA Rennes, Inst Sci Chim Rennes, Rennes, France.
    Candolfi, C.
    Univ Lorraine, CNRS, UMR 7198, Inst Jean Lamour, Nancy, France; Univ Lorraine, UMR 7198 CNRS, Inst Jean Lamour, Nancy, France.
    Lenoir, B.
    Univ Lorraine, CNRS, UMR 7198, Inst Jean Lamour, Nancy, France; Univ Lorraine, UMR 7198 CNRS, Inst Jean Lamour, Nancy, France.
    Effect of Ag Doping on Electronic Structure of Cluster Compounds AgxMo9Se11 (x = 3.4, 3.9)2018In: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 1, no 8, p. 4032-4039Article in journal (Refereed)
    Abstract [en]

    The electronic structure of AgxMo9Se11 as a potential material for thermoelectric applications was studied using high-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) and the resonant inelastic X-ray scattering (RIXS) technique. The experiments were supported by first-principle calculations using density functional theory (DFT). The analysis of obtained spectra indicate the presence of subvalent (less than 1+) Ag in AgxMo9Se11. The advanced HERFD-XAS measurements allowed us to resolve the contribution of the electronic states at the Fermi level of AgxMo9Se11 and to monitor its dependence on the x value. A comparison of the experimental data with the results of the DFT calculations suggests the importance of the Ag2-type sites with the shortest Ag–Se distance for affecting the properties of AgxMo9Se11.

  • 278.
    Bárdos, Ladislav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cold atmospheric plasma: Sources, processes, and applications2010In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, no 23, p. 6705-6713Article in journal (Refereed)
    Abstract [en]

    Atmospheric pressure gas discharge plasmas, especially those operated at energy non-equilibrium and low gas temperatures, have recently become a subject of great interest for a wide variety of technologies including surface treatment and thin-film deposition. A driving force for these developments is the avoidance of expensive equipment required for competing vacuum-based plasma technologies. Although there are many applications where non-equilibrium (cold) plasma at atmospheric and higher pressures represents a substantial advantage, there are also a number of applications where low-pressure plasmas simply cannot be replaced due to specific properties and limitations of the atmospheric plasma and related equipment. In this critical review, the primary principles and characteristics of the cold atmospheric plasma and differences from vacuum-based plasma processes are described and discussed to provide a better understanding of the capabilities and limits of emerging atmospheric plasma technologies.

  • 279.
    Bárdos, Ladislav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cold Atmospheric Plasma Treatment of Inner Surfaces of Pipes2012Conference paper (Refereed)
  • 280.
    Bárdos, Ladislav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cold Atmospheric Plasma Treatment of Steel Buoys for Wave Energy Converters2011In: Plasma Processes and Polymers, ISSN 1612-8850, E-ISSN 1612-8869, Vol. 8, no 7, p. 658-663Article in journal (Refereed)
    Abstract [en]

    Steel sheets used for ocean buoys in the linear wave energy converters have been treated by cold atmospheric plasmas in Ar, Ne, and the wet air. The contact angle has decreased from about 48 degrees at an untreated surface to a minimum of about 248, depending on the plasma and the treatment time. This corresponds to an increase of the surface energy from about 57 to 69 mN/m. Comparison of the XPS spectra before and after plasma treatment confirmed important role of the plasma activated oxygen. The hydrophilicity of treated surfaces deteriorates within about 120 min. Immediate painting of treated surfaces has lead to considerable better paint adhesion than on untreated surfaces. The plasma treatment of buoys before painting is, therefore, expected to improve their corrosion resistance and lifetime.

  • 281.
    Bárdos, Ladislav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Surface Treatment of Energy Conversion Device Components by Cold atmospheric Plasma: Paper SE+PS-MoM32010In: AVS 57th Int. Symposium, Albuquerque, New Mexico, 2010Conference paper (Refereed)
  • 282.
    Bárdoš, Ladislav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cold Atmospheric Plasma Deposition of Diamond2007In: Plasma Processes and Polymers, ISSN 1612-8850, Vol. 4, no 5, p. 511-514Article in journal (Refereed)
    Abstract [en]

    Nanocluster diamonds can be synthesized in open air on stainless steel and molybdenum substrates with a hybrid cold atmospheric plasma source using air plasma and an air + alcohol mixture. At microwave powers below 300 W and at gas flow rates below 300 sccm the temperature of a thermally insulated steel substrate placed 1.5 cm from the hollow cathode caused by the air plasma were less than 600 °C. 200 nm thick coatings with nanocluster diamond grains and aggregates exhibiting diamond peaks in the Raman spectra at 1 325 cm-1 on stainless steel and at 1 322 cm-1 on Mo were formed after 1 h on untreated substrates.

  • 283.
    Bäckbro, Hannes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A study of potential approaches to simulate power output as well as identifying anomalous operation of wind turbines2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    From an economical perspective, ice accretion on wind turbines located in cold climates can cause severe and costly production losses. To reduce the cost caused by such factors, it is important to early detect anomalous operation. This requires the knowledge of expected operation for all possible states of operation. The purpose of this M.Sc. thesis was first of all to investigate the feasibility to define a model able to simulate expected power output regardless time of the year. A second purpose was to investigate possible approaches for the identification of wind turbines deviating from expected operation. Regarding the first purpose, two different models were developed to investigate the possibility to simulate expected power output. A deterministic model based on the characteristic power curve and a non-deterministic regression tree model based on machine learning algorithms. As regards the second model, two control charts were implemented and their ability to identify abnormal operation was evaluated. The development and evaluation of the models as well as the control charts were performed in Matlab R2013b.

  • 284.
    Bäcklund, Annika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fotogrammetrisk analys av kornstorleksfördelningeni erosionsskydd vid kraftverksdammar2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis was made to investigate the possibilities of using the Matlab-basedsoftware Basegrain to determine grain size distributions of erosion protections onhydropower dams. Basegrain is a photogrammetric tool developed to generate grainsize distributions and other information about coarse flood sediments by analyzing adigital photo of the stone bed. The investigation was made by validating the ability forBasegrain to assess grain size distributions of various materials smaller than the blocksused in an erosion protection by comparing sieving results or manual measurementswith the results obtained by the program. A statistical comparison was then made bycomparing the results from sieving and the program. The possibilities of using thesame method on existing hydropower dams were then investigated by determiningwhether the method was practically viable or not.The results showed that Basegrain generated grain size distributions for coarse gravelthat were very close to the sieving results. It also provided grain size distributions forlarger fractions of stones quite close to the results made by measuring the diameterof the stones by hand. The results also showed it was possible to use the samemethod on existing erosion protections on hydropower dams and obtain grain sizedistributions.

  • 285. Bäckström, Mats
    et al.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Månsson, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundén, Olof
    Nilsson, T
    Some Recent Work on Intentional EMI in Sweden2008Conference paper (Refereed)
  • 286. Båverman, Gabriel
    et al.
    Tavoosi, Edris
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of a solar powered water pumping system in Mutomo, Kenya: Comparison between a submersible induction motor and a PMSM system2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An existing solar-powered water pumping system located in Mutomo, Kenya has beenevaluated in this paper. The requirement for this system is to produce a minimum of25m³ water per day throughout the year.The aim of this thesis is to investigate theperformance of the currently installed system and find a suitable replacement in termsof efficiency and economic viability. In order to acquire the necessary knowledge forthis project, a literature study was carried out to analyse the research within the area.Three simulation models were created which all include an electric motor driven by aphotovoltaic array and are connected to a submersible groundwater pump. Allmodels utilise space vector pulse width modulation. One model of an inductionmotor that represents the currently installed system, one induction motor thatdelivers a minimum of 25 m³ water per day, and one model of a permanent magnetsynchronous motor for comparison. Simulations using weather data, representing anaverage day for each month of the year were carried out. It was shown that thecurrently installed system does not fulfil the requirement of producing 25 m³ waterper day, and in addition produces a significant amount of energy that can not beutilised. It was also shown that the efficiency of the permanent magnet synchronousmotor was superior to the induction motors. In order to compare the systems interms of economic viability, price quotations from world leading manufacturers wereacquired. The results of the economic comparison show that the superior efficiencyof the permanent magnet synchronous motor was not enough to compensate for thehigher investment cost.

  • 287.
    Bülow, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Generator Perspective on Vertical Axis Wind Turbines2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The wind energy conversion system considered in this thesis is based on a vertical axis wind turbine with a cable wound direct drive PM generator. Diode rectifiers are used to connect several such units to a single DC-bus and a single inverter controls the power flow from the DC-bus to a utility grid. This work considers the described system from a generator perspective i.e. the turbine is primarily seen as a torque and the inverter is seen as a controlled load.

    A 12 kW VAWT prototype with a single turbine has been constructed within the project. The power coefficient of this turbine has been measured when the turbine is operated at various tip speed ratios. This measurement determines both how much energy the turbine can convert in a given wind and at what speed the turbine should be operated in order to maximise the energy capture. The turbine torque variation during the revolution of the turbine has also been studied.

    A PM generator prototype has been constructed in order to study power loss in the stator core at low electrical frequencies. Heat exchange between the stator and the air-gap between the stator and the rotor has been studied. Heat exchange between the stator and the air-gap is increased by turbulence caused by the rotor. The generator was also used in a demonstration of a DC-grid where two diode rectified PM generators supplied power to a single DC load.  An initial study of an inverter suitable for grid connection of the 12 kW PM generator has been performed.

    Several turbine control strategies are evaluated in simulations. The control strategies only require the parameter "turbine speed" to determine the optimal system load.

  • 288.
    Bülow, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Extreme Load Conditions for Wind Powered Direct Drive PM Generators2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wind energy is a rapidly growing energy source with vast potential. Vertical axis wind turbines could be more cost-effective than the three bladed horizontal axis turbines that dominate today. A concept based on the straight bladed Darrieus turbine together with a PMgenerator operating in direct drive is studied at Uppsala University; this thesis is a part of that project. This thesis contains a study of stator core loss at low electrical frequencies. The purpose of the study was to test the reliability of core loss simulations where the specific loss at low frequency is extrapolated using specific loss at 50Hz. The simulated loss was compared to the measured loss. Passive rectifiers can be used to connect all wind energy converters in a wind farm to a mutual DC load. This principle has been demonstrated using two PM generators with very different properties. This thesis also contains two studies of a full vertical axis wind turbine prototype. The first study concerns the power coefficient of the turbine. The power coefficient was measured at several wind speeds and turbine rotational speeds. The power coefficient attains its maximum value of 29% when the tip speed ratio is 3.3. In a second study, the armature currents of the generator were used to map the harmonic content of the turbine torque. The third harmonic of the turbine torque was found to be the strongest harmonic. This thesis also presents a wind energy converter that has been tailored for a telecom tower. Several aspects of the design are unique.

  • 289.
    Bülow, Fredrik
    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.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stator cooling by axial flow through air-gap of high torque PM generator.Manuscript (preprint) (Other academic)
  • 290.
    Bülow, Fredrik
    et al.
    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.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    No-load core loss prediction of PM generator at low electrical frequency2012In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 43, p. 389-392Article in journal (Refereed)
    Abstract [en]

    A method for measurement of frequency dependent electromagnetic core loss of a permanent magnet generator is presented. Core loss of a PM generator is measured at electrical frequencies ranging from 4 to 14 Hz. Core loss in the same interval is simulated using the finite element method and frequency domain loss separation. The specific loss is both extrapolated from specific loss at 50 Hz and measured directly at 4, 8, 12 and 16 Hz. Core loss simulations based on extrapolated specific loss are 38–53% smaller than measured loss. Core loss simulations based on specific loss measured at 4, 8, 12 and 16 Hz are 19–23% smaller than measured loss.

  • 291.
    Bülow, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjellin, Jon
    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.
    Torque ripple of a straight-bladed Darrieus turbine with PM generator estimated from diode rectifier output current.Manuscript (preprint) (Other academic)
  • 292.
    Bülow, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjellin, Jon
    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.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ström, P
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Adapting a VAWT with PM generator to telecom applications2010In: European Wind Energy Conference & Exhibition, Warsaw, Poland, 2010Conference paper (Refereed)
  • 293.
    Cahlenstein, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Transparent solar cell techniques: A profitability study2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is intended to investigate the profitability of transparent solar windows which concentrates parts of the invisible light to a solar cell.This makes it possible to generate electric energy while the window still is transparent. Other gains apply such as the removal of solar radiation into the building which makes it possible to decrease the amount of energy needed for cooling. The study will investigate profitability of transparent solar windows by simulating energy used for heating and cooling and by investigating profitability of the produced energy. The results show that it is not economically justified to use transparent solar windows for electricity generation with present techniques and with Swedish climate. It is however economically justified to use as a isolating window in buildings.

    The master thesis has been completed at Skanska in Stockholm.

  • 294.
    Caleman, Carl
    et al.
    Physik Department E17, Technische Universität München.
    Ortiz, Carlos
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Marklund, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
    Bultmark, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Gabrysch, Markus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Parak, F. G.
    Hajdu, Janos
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Timneanu, Nicusor
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
    Radiation damage in biological material: electronic properties and electron impact ionization in urea2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, no 1, p. 18005-Article in journal (Refereed)
    Abstract [en]

    Radiation damage is an unavoidable process when performing structural investigations of biological macromolecules with X-rays. In crystallography this process can be limited through damage distribution in a crystal, while for single molecular imaging it can be outrun by employing short intense pulses. Secondary electron generation is crucial during damage formation and we present a study of urea, as model for biomaterial. From first principles we calculate the band structure and energy loss function, and subsequently the inelastic electron cross-section in urea. Using Molecular Dynamics simulations, we quantify the damage and study the magnitude and spatial extent of the electron cloud coming from an incident electron, as well as the dependence with initial energy.

  • 295.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Current Resource Assessment: Measurements and Characterization2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing interest in converting energy from renewable resources into electricity has led to an increase in research covering the field of marine current energy, mainly concerning tidal currents and in-stream tidal turbines. Tides have the advantage of being predictable decades ahead. However, the tidal resource is intermittent and experiences local variations that affect the power output from a conversion system. The variability is mainly due to four aspects: the tidal regime, the tidal cycle, bathymetry at the site and weather effects. Each potential site is unique, the velocity flow field at tidal sites is highly influenced by local bathymetry and turbulence. Hence, characterizing the resource requires careful investigations and providing high quality velocity data from measurement surveys is of great importance. In this thesis, measurements of flow velocities have been performed at three kinds of sites.

    A tidal site has been investigated for its resource potential in one of all of the numerous fjords in Norway. Measurements have been performed to map the spatial and temporal variability of the resource. Results show that currents in the order of 2 m/s are present in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus have potential for in-stream energy conversion. A model is proposed that predicts peak current speed from information on tidal range at the site. A corresponding model can be set up and implemented at other similar sites affected by tides, i.e. fjord inlets connecting the ocean to a fjord or a basin.

    A river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydrokinetic power plant nearby, making the site suitable for experiments on the performance of the vertical axis turbine in its natural environment. The turbine has been run in uniform flow and measurements have been performed to characterize the extent of the wake.

    An ocean current site was a target of investigation for its potential for providing utilizable renewable energy. A measurement campaign was conducted, mapping the flow both spatially and temporally. However, the site was shown to not be suitable for energy conversion using present technique.

  • 296.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Potentialbedömning av marin strömkraft i Finnhamn: Fältmätningar och resultat2015Report (Other academic)
    Abstract [sv]

    På uppdrag av Skärgårdsstiftelsen utfördes mätningar av vattenhastigheten utanför Finnhamn i syfte att undersöka potentialen för att installera och driva ett marint strömkraftverk på platsen. Denna rapport presenterar resultaten från den undersökningen som genomförts med tvärsnittsmätningar och långtidsmätningar av vattenhastigheterna. Resultaten visar på låga vattenhastigheter under mätperioden. Slutsatsen är att platsen inte har tillräckligt stor energipotential för att vara av intresse för utbyggnad av strömkraftverk utifrån den teknik som finns idag.

  • 297.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Resource characterization and variability studies for marine current power2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Producing electricity from marine renewable resources is a research area that develops continuously. The field of tidal energy is on the edge to progress from the prototype stage to the commercial stage. However, tidal resource characterization, and the effect of tidal turbines on the flow, is still an ongoing research area in which this thesis aims to contribute.

    In this thesis, measurements of flow velocities have been performed at three kinds of sites. Firstly, a tidal site has been investigated for its resource potential in a fjord in Norway. Measurements have been performed with an acoustic Doppler current profiler to map the spatial and temporal characteristics of the flow. Results show that currents are in the order of 2 m/s in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus has potential for in-stream energy conversion. Secondly, a river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydro power plant, making the site suitable for experiments on the performance of the vertical axis turbine in a natural environment. The turbine was run in steady discharge flows and measurements were performed to characterize the extent of the wake. Lastly, at an ocean current site, the effect that transiting ferries may have on submerged devices was investigated. Measurements were conducted with two sonar systems to obtain an underwater view of the wake caused by a propeller and a water jet thruster respectively.

    Furthermore, the variability of the intermittent renewable sources wind, solar, wave and tidal energy was investigated for the Nordic countries. All of the sources have distinctly different variability features, which is advantageous when combining power generated from them and introducing it on the electricity grid. Tidal variability is mainly due to four aspects: the tidal regime, the tidal cycle, local bathymetry causing turbulence, asymmetries etc. and weather effects. Models of power output from the four sources was set up and combined in different energy mixes for a “highly renewable” and a “fully renewable” scenario. By separating the resulting power time series into different frequency bands (long-, mid-, mid/short-, and short-term components) it was possible to minimize the variability on different time scales. It was concluded that a wise combination of intermittent renewable sources may lower the variability on short and long time scales, but increase the variability on mid and mid/short time scales.

    The tidal power variability in Norway was then investigated separately. The predictability of tidal currents has great advantages when planning electricity availability from tidal farms. However, the continuously varying tide from maximum power output to minimum output several times per day increases the demand for backup power or storage. The phase shift between tidal sites introduces a smoothing effect on hourly basis but the tidal cycle, with spring and neap tide simultaneously in large areas, will inevitably affect the power availability.

  • 298.
    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.

  • 299.
    Carpman, Nicole
    et al.
    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.
    Tidal current phasing along the coast of Norway2016Conference paper (Refereed)
    Abstract [en]

    Tidal currents provide an intermittent source of renewable energy. A high degree of intermittency is unfavorable in the existing power system. However, by aggregating tidal power from sites with variable tidal phase a more firm power outpu tmay be achieved. In this paper, the tidal current phasing between 114 potential tidal energy sites along the Norwegian coast is investigated. Time series of tidal currents are generated with a model that considers the variation in current strength due to the variability in the semi-diurnal tidal cycle (spring to neap, flood to ebb, first to second daily tide etc.). From these, available kinetic energy in the natural flow is calculated. A constant conversion rate is then applied to give the power output at each site. Three scenarios, with varying number of sites and energy extraction, are investigated. The variability in each scenario is quantified on different time scales by filtering the aggregated power and calculate standard deviation and step change. It is found that the variability can be lowered by choosing sites with an advantageous time lag and limit the power output from the most energetic sites. As expected, smoothing is most distinct on short time scales.

  • 300.
    Carpman, Nicole
    et al.
    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.
    Tidal resource characterization in the Folda Fjord, Norway2016In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, p. 27-44Article in journal (Refereed)
    Abstract [en]

    For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

3456789 251 - 300 of 1771
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • 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