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  • 1.
    Anttila, Sara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cardoso da Silva Júnior, Dalmo
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Parwal, Arvind
    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.
    Power Control Strategies for a Smoother Power Output from a Wave Power Plant2019Conference paper (Refereed)
    Abstract [en]

    This paper presents power output and power control strategies for a wave power plant. Three cases are presented; active power output without power smoothing control, active power output with an energy storage to smooth the power output to the grid, active- and reactive power control using the grid side inverter and an energy storage. The model is constructed in MATLAB Simulink and is based on the wave energy converter technology developed at Uppsala University. The model input is wave height data from the Wave Hub test site, UK. The study show that without power control, the output power is fluctuating significantly during a 60 second time period. The difference between the average power output and the maximum power peaks can be as high as a factor of 6. By using an energy storage a significant reduction of the power fluctuation, to approximately ± 10 %, can be achieved. Even with the high intermittency of the input power, it is possible to control the active- and reactive power output to the grid. Thus, it is shown that it is possible to provide grid support functions, which are needed in the transition to a higher penetration of renewable energy sources on the grid.

  • 2. Anttila, Sara
    et al.
    Silva, Dalmo
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Parwal, Arvind
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power Control Strategies for a Smoother Power Output from a Wave Power Plant2019In: 13th European Wave and Tidal Energy Conference (EWTEC), Napoli, Italy, September 1-6, 2019, Napoli, Italy: European Wave and Tidal Energy Conference , 2019Conference paper (Refereed)
  • 3.
    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.
    Thermal modelling of a passively cooled inverter for wave power2015In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 9, no 4, p. 389-395Article in journal (Refereed)
    Abstract [en]

    Owing to very costly maintenance operations, the reliability of electrical systems for offshore renewable energy is a major issue to make electricity production economical. Therefore proper thermal management is essential in order to avoid the components from being damaged by excessive temperature increase. Both analytic and computational fluid dynamics (CFD) models were implemented to assess the temperature increase in the inverter installed in a submerged substation and during working conditions. It was shown that this inverter could transmit a total power of up to about 35 kW. This limit is dependent on a certain distance between the modules and a perfect thermal contact with the hull. The influence of several of such parameters as well as the efficiency of passive cooling were studied.

  • 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.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, France..
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimized distribution of a large number of power electronics components cooled by conjugate turbulent natural convection2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 124, p. 975-985Article in journal (Refereed)
    Abstract [en]

    Natural convection allows for passive cooling which is used in many engineering applications. Placing dissipating components on a common vertical heatsink can be optimized to give the best possible cooling capacity. In this study, a numerical model for three-dimensional conjugated convective and conductive heat transfer was used to evaluate the distribution of up to 36 flush-mounted rectangular heaters. The temperature profiles and the heat fluxes were compared with experimental data for validation. The dissipated power was set as an input parameter and the optimal distribution was selected as the one with the lowest temperature elevation. Two different heuristics-a geometric parameter and an artificial neural network-were proposed and evaluated as alternatives to heavy CFD calculations.

  • 7.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, Chassencuil, France.
    Zhu, Bo
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, Chassencuil, France.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 11, article id 912Article in journal (Refereed)
    Abstract [en]

    Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two.

  • 8.
    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.

  • 9.
    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.

    List of papers
    1. Wave Energy from the North Sea: Experiences from the Lysekil Research Site
    Open this publication in new window or tab >>Wave Energy from the North Sea: Experiences from the Lysekil Research Site
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    2008 (English)In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, p. 221-240Article, review/survey (Refereed) Published
    Abstract [en]

    This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

    Keywords
    Wave power, Renewable energy, Sea trial, Linear generator, Point absorber, Environmental impact
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-107215 (URN)10.1007/s10712-008-9047-x (DOI)000260967900002 ()
    Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2017-12-13Bibliographically approved
    2. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
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    2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed) Published
    Abstract [en]

    The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
    3. Ocean wave energy absorption in response to wave period and amplitude: offshore experiments on a wave energy converter
    Open this publication in new window or tab >>Ocean wave energy absorption in response to wave period and amplitude: offshore experiments on a wave energy converter
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    2011 (English)In: IET Renewable Power Generation, ISSN 1752-1416, Vol. 5, no 6, p. 465-469Article in journal (Refereed) Published
    Abstract [en]

    The ability of a wave energy converter to capture the energy of ocean waves has been studied in offshore experiments. This study covers 50 days during which the converter was subjected to ocean waves over a wide range of frequencies and amplitudes as well as three different electrical loads. The results present the wave energy converter??s energy absorption as a function of significant wave height, energy period and electrical load. It is shown that the power generated overall continues to increase with wave amplitude, whereas the relative absorption decreases towards the highest periods and amplitudes. The absorption reached a maximum of approximately 24% with the used combination of buoy, generator and electrical load. Absorption to cover for iron and mechanical losses has not been included. A brief study of the nature of the electromagnetic damping force has also been included in the study. The wave energy converter is of the technology that is being researched at Uppsala University and experimented on off the Swedish west coast at the Lysekil wave energy research site.

    Place, publisher, year, edition, pages
    IEEE Press, 2011
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-165034 (URN)10.1049/iet-rpg.2010.0124 (DOI)000303376900007 ()
    Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2013-05-17Bibliographically approved
    4. Experimental results of rectification and filtration from an offshore wave energy system
    Open this publication in new window or tab >>Experimental results of rectification and filtration from an offshore wave energy system
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    2009 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 34, no 5, p. 1381-1387Article in journal (Refereed) Published
    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.

    Keywords
    Wave energy conversion, Electric rectifiers, Energy conversion, Experiments, Porous materials, Power takeoffs, Takeoff
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112941 (URN)10.1016/j.renene.2008.09.010 (DOI)000263608500026 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-12-12Bibliographically approved
    5. Study of aWave Energy Converter Connected to a Nonlinear Load
    Open this publication in new window or tab >>Study of aWave Energy Converter Connected to a Nonlinear Load
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    2009 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 2, p. 123-127Article in journal (Refereed) Published
    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.

    Keywords
    ocean waves
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112947 (URN)10.1109/JOE.2009.2015021 (DOI)000266245600004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-12-12Bibliographically approved
    6. Experimental Results From an Offshore Wave Energy Converter
    Open this publication in new window or tab >>Experimental Results From an Offshore Wave Energy Converter
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    2010 (English)In: 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) Published
    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.

    Keywords
    ocean wave power, linear generators, conversion systems, experimental results
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-133599 (URN)10.1115/1.4001443 (DOI)000283325300003 ()
    Available from: 2010-11-15 Created: 2010-11-11 Last updated: 2017-12-12Bibliographically approved
    7. Operation analysis of a wave energy converter under different load conditions
    Open this publication in new window or tab >>Operation analysis of a wave energy converter under different load conditions
    2011 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 5, no 3, p. 245-250Article in journal (Refereed) Published
    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.

    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-140111 (URN)10.1049/iet-rpg.2010.0153 (DOI)000303375900004 ()
    Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
    8. A wave power unit
    Open this publication in new window or tab >>A wave power unit
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    2009 (English)Patent (Other (popular science, discussion, etc.))
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-140112 (URN)
    Patent
    WO 2010/085188 (2010-07-29)
    Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2016-04-14Bibliographically approved
    9. Design proposal of electrical system for linear generator wave power plants
    Open this publication in new window or tab >>Design proposal of electrical system for linear generator wave power plants
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    2009 (English)In: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS, IEEE , 2009, p. 4180-4185Conference paper, Published 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.

    Place, publisher, year, edition, pages
    IEEE, 2009
    Keywords
    electrical system layout, linear generator wave power plants, marine substations, wave energy converters
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112956 (URN)10.1109/IECON.2009.5414903 (DOI)000280762001321 ()978-1-4244-4648-3 (ISBN)978-1-4244-4650-6 (ISBN)
    Conference
    35th Annual Conference of the IEEE-Industrial-Electronics-Society (IECON 2009), Porto, PORTUGAL, NOV 03-05, 2009
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
    10. Offshore underwater substation for wave energy converter arrays
    Open this publication in new window or tab >>Offshore underwater substation for wave energy converter arrays
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    2010 (English)In: IET Renewable Power Generation, ISSN 1752-1416, Vol. 4, no 6, p. 602-612Article in journal (Refereed) Published
    Abstract [en]

    In this study, the design, construction, deployment and operation of an offshore underwater substation is discussed. The seabed placed substation interconnects three linear generator wave energy converters (WECs) at the Swedish Lysekil wave energy research site. The power from the WECs fluctuates because of their direct-driven topology. The generator voltage has varying electrical frequency and amplitude. To reduce the fluctuations, the individual voltages of the WECs are rectified and the power is added on a common DC-bus in the substation. The voltage is inverted, transformed and power is transmitted to an on-shore resistive load. The substation was retrieved on two occasions since the deployment in the spring of 2009. The functionality of the substation is validated by comparing voltage and current wave forms from Simulink with measured results from laboratory experiments. In addition, a sample of results from real offshore operation is illustrated and discussed. With a proportional-integral-derivative (PID)-regulator in the inverter control, the small fluctuations in the DC-bus voltage could be minimised. However, this would reduce the energy storage capability of the DC-link smoothing capacitors.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112954 (URN)10.1049/iet-rpg.2009.0180 (DOI)000284511300013 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2018-05-31Bibliographically approved
    11. Description of the control and measurement system used in the Low Voltage Marine Substation at the Lysekil research site
    Open this publication in new window or tab >>Description of the control and measurement system used in the Low Voltage Marine Substation at the Lysekil research site
    2009 (English)In: Proc of the 8th European Wave and Tidal Energy Conference, EWTEC 2009, Uppsala, 2009, p. 44-50Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Uppsala: , 2009
    Identifiers
    urn:nbn:se:uu:diva-112953 (URN)
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2011-03-11
    12. Temperature measurements in a linear generator and marine substation for wave power
    Open this publication in new window or tab >>Temperature measurements in a linear generator and marine substation for wave power
    Show others...
    2012 (English)In: 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) Published
    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.

    Keywords
    convection, linear machines, machine insulation, machine windings, offshore installations, power convertors, stators, substations, temperature measurement, wave power generation
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-140113 (URN)10.1115/1.4004629 (DOI)000308596500021 ()
    Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
    13. Experimental results from the operation of aggregated wave energy converters
    Open this publication in new window or tab >>Experimental results from the operation of aggregated wave energy converters
    Show others...
    2012 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 6, no 3, p. 149-160Article in journal (Refereed) Published
    Abstract [en]

    Wave energy comes in pulses and is unsuitable for direct conversion and transmission to the grid. One method to smooth the power is to deploy arrays of wave energy converters (WECs), the geometrical layout and damping optimisation of which many have studied analytically and numerically, but very few by experiments at sea. In this study, the standard deviation of electrical power as function of various parameters is investigated. Two offshore experiments have been conducted. During the longer run, three WECs were operated in linear damping during 19.7 days. It is shown that the standard deviation reduces with the number of WECs in the array up to three WECs. The reduction compared to single WEC operation was found here to be 30 and 80% with two and three WECs, respectively, as a mean for an arbitrary array member. It is found that in sea states above ~2 kW/m, the standard deviation is independent of sea state parameters. This is contradictory to a previous study on the same device. The results are, however, in accordance with numerical results of the SEAREV device but show larger reduction in standard deviation with number of WECs. This could be because of suboptimal damping conditions.

    Keywords
    offshore installations, power convertors, power grids, wave power generation, SEAREV device, WEC, aggregated wave energy converters operation, arbitrary array member, damping optimisation, direct conversion, direct transmission, electrical power standard deviation, geometrical layout, linear damping, offshore experiments, power grid, sea state parameters
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-140114 (URN)10.1049/iet-rpg.2010.0234 (DOI)
    Funder
    StandUp
    Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
    14. Linear generator connected to a resonance circuit
    Open this publication in new window or tab >>Linear generator connected to a resonance circuit
    (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-140115 (URN)
    Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
  • 10.
    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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    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

  • 14.
    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.

  • 15.
    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.

  • 16.
    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    Ekström, Rickard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kurupath, Venugopalan
    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.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluating Constant DC-Link Operation of Wave Energy Converter2012In: Proceedings of the 31st ASME International Conference on Ocean, Offshore and Arctic Engineering, vol. 7, 2012, p. 269-276Conference paper (Refereed)
    Abstract [en]

    A Wave Energy Converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common DC-bus. The DC voltage level seen by the generator is directly linked to the electromagnetic damping of the generator A lower DC-level results in a higher damping factor and is important for increased absorption of the wave power The drawback is increased losses in generator windings and cable resistance. There will be an optimal DC-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the DC-level seen by the generator influence the power output. The results indicate that higher DC-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which DC-level is chosen.

  • 21.
    Ekström, Rickard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kurupath, Venugopalan
    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.
    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.
    Evaluating Constant DC-Link Operation of Wave Energy Converter2014In: Journal of Dynamic Systems Measurement, and Control, ISSN 0022-0434, E-ISSN 1528-9028, Vol. 136, no 1, p. 014501-Article in journal (Refereed)
    Abstract [en]

    A wave energy converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common dc-bus. The dc voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower dc-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal dc-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the dc-level seen by the generator influence the power output. The results indicate that higher dc-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which dc-level is chosen.

  • 22.
    Francisco, Francisco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    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.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Power as Solution for Off-Grid Water Desalination Systems: Resource Characterization for Kilifi-Kenya2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 4, article id 4Article in journal (Refereed)
    Abstract [en]

    Freshwater scarcity is one of humanity's reoccurring problems that hamper socio-economic development in many regions across the globe. In coastal areas, seawater can be desalinated through reverse osmosis (RO) and transformed into freshwater for human use. Desalination requires large amounts of energy, mostly in the form of a reliable electricity supply, which in many cases is supplied by diesel generators. The objective of this work is to analyze the wave power resource availability in Kilifi-Kenya and evaluate the possible use of wave power converter (WEC) to power desalination plants. A particular focus is given use of WECs developed by Uppsala University (UU-WEC). The results here presented were achieved using reanalysis-wave data revealed that the local wave climate has an approximate annual mean of 7 kW/m and mode of 5 kW/m. Significant wave height and wave mean period are within 0.8-2 m and 7-8 s respectively, with a predominant wave mean direction from southeast. The seasonal cycle appeared to be the most relevant for energy conversion, having the highest difference of 6 kW/m, in which April is the lowest (3.8 kW/m) and August is the peak (10.5 kW/m). In such mild wave climates, the UU-WEC and similar devices can be suitable for ocean energy harvesting for water desalination systems. Technically, with a capacity factor of 30% and energy consumption of 3 kWh/m(3), a coastal community of about five thousand inhabitants can be provided of freshwater by only ten WECs with installed capacity of 20 kW.

  • 23.
    Hong, Yue
    et al.
    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.
    Castellucci, Valeria
    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.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linear generator-based wave energy converter model with experimental verification and three loading strategies2016In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 3, p. 349-359Article in journal (Refereed)
    Abstract [en]

    Within the Lysekil wave energy research project at the Swedish west coast, more than ten Wave Energy Converters (WECs) prototypes have been developed and installed in an ocean based test site. Since 2006 various experiments have been conducted and the generated electricity was delivered to shore at a nearby island. While experiments are essential for the development of wave energy converters, theoretical studies and simulations are an important complement – not only in the search for advanced designs with higher efficiency, but also for improving the economic viability of the studied concepts. In this paper a WEC model is presented. The model consists of three subsystems: i) the hydrodynamic source, ii) the linear generator model, and iii) the electrical conversion system. After the validation with the experimental results at the research site, the generator model is connected to three passive load strategies – linear resistive load, passive rectification and resonance circuit. The paper focuses on analysing the operation of the model coupled with three load cases. The results prove that the WEC model correctly simulates the linear generator developed in the Lysekil Project. Moreover, the comparison among different load cases is made and discussed. The results gives an indication of the efficiency of energy production as well as the force ripples and resulting mechanical loads on the wave energy converters.

  • 24.
    Hong, Yue
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hultman, Erik
    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.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjökvist, Linnea
    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.
    Krishna, Remya
    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.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lindblad, Liselotte
    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.
    Käller, Daniel
    Rahm, 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.
    Boström, Cecilia
    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.
    Status Update of the Wave Energy Research at Uppsala University2013Conference paper (Refereed)
  • 25.
    Hong, Yue
    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.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Engström, Jens
    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.
    Review on electrical control strategies for wave energy converting systems2014In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 31, p. 329-342Article, review/survey (Refereed)
    Abstract [en]

    Renewable energy techniques are now gaining more and more attention as the years pass by, not only because of the threat of climate change but also, e.g. due to serious pollution problems in some countries and because the renewable energy technologies have matured and can be depended upon an increasing degree. The energy from ocean waves bares tremendous potential as a source of renewable energy, and the related technologies have continually been improved during the last decades. In this paper, different types of wave energy converters are classified by their mechanical structure and how they absorb energy from ocean waves. The paper presents a review of strategies for electrical control of wave energy converters as well as energy storage techniques. Strategies of electrical control are used to achieve a higher energy absorption, and they are also of interest because of the large variety among different strategies. Furthermore, the control strategies strongly affect the complexity of both the mechanical and the electrical system, thus not only impacting energy absorption but also robustness, survivability, maintenance requirements and thus in the end the cost of electricity from ocean waves.

  • 26.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Anttila, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Frost, Anna E.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kontos, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Engström, Jens
    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.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Renewable Energy Sources for Desalination, Generating Freshwater and Lithium2019Conference paper (Refereed)
  • 27.
    Leijon, Jennifer
    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.
    Freshwater production from the motion of ocean waves - A review2018In: Desalination, ISSN 0011-9164, E-ISSN 1873-4464, Vol. 435, p. 161-171Article, review/survey (Refereed)
    Abstract [en]

    Freshwater scarcity and insufficient sanitation are global urgent problems, affecting billions of people. In this review paper, the process of desalination powered by wave power has been investigated as a potential sustainable solution to water shortage. The different desalination techniques suitable for this type of combined system, i.e. reverse osmosis, electrodialysis and mechanical vapor compression, have been outlined, as well as the different wave energy converters possible to power the desalination process, i.e. oscillating water columns, oscillating bodies (wave activated bodies) and overtopping systems. Some necessary considerations for this type of project are identified. The different wave power/desalination projects and how they have proceeded are presented. The most common design of a wave energy and desalination system includes a wave activated body to pressurize seawater; the seawater flows through a reverse osmosis membrane, resulting in freshwater. Some successful (freshwater producing) wave energy/desalination projects were identified: Delbuoy, the oscillating water column in Vizhinjam, CETO Freshwater, SAROS and Odyssee. It is concluded that wave power and desalination can be combined in a sustainable and autonomous system, generating freshwater from the ocean waves. However, questions regarding cost of produced water, variations in power production due to intermittency and environmental effects still remain.

  • 28.
    Leijon, Jennifer
    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.
    Lärarens arbete mot utveckling av generiska färdigheter och variation i teknikvetenskaplig utbildning genom relationsskapande åtgärder2019In: Högre Utbildning, ISSN 2000-7558, E-ISSN 2000-7558, Vol. 9, no 1Article in journal (Refereed)
  • 29.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Forslund, Johan
    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.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Current Energy Converters to Power a Reverse Osmosis Desalination Plant2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 11, article id 2880Article in journal (Refereed)
    Abstract [en]

    Some countries are facing issues on freshwater and electricity production, which can be addressed with the use of renewable energy powered desalination systems. In the following study, a reverse osmosis desalination plant powered by marine current energy converters is suggested. The marine current energy converters are designed at Uppsala University in Sweden, specifically for utilizing low water speeds (1–2 m/s). Estimations on freshwater production for such a system, in South Africa, facing the Indian Ocean was presented and discussed. It is concluded that the desalination plant cannot by itself supply freshwater for a population all the time, due to periods of too low water speeds (<1 m/s), but for 75% of the time. By using ten marine current energy converters, each with a nominal power rating of 7.5 kW, combined with a reverse osmosis desalination plant and water storage capacity of 2800 m3, it is possible to cover the basic freshwater demand of 5000 people. More studies on the hydrokinetic resource of the Western Indian Ocean, system cost, technology development, environmental and social aspects are necessary for more accurate results.

  • 30.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjölund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergard, Boel
    Seabased Ind AB, Verkstadsgatan 4, S-45330 Lysekil, Sweden..
    Boström, Cecilia
    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.
    Temiz, 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.
    Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 1, article id 84Article in journal (Refereed)
    Abstract [en]

    The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe14B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper.

  • 31.
    Leijon, Mats
    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.
    Danielsson, Oskar
    Gustafsson, Stefan
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Langhamer, Olivia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Strömstedt, Erland
    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.
    Sundberg, Jan
    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.
    Tyrberg, Simon
    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.
    Wave Energy from the North Sea: Experiences from the Lysekil Research Site2008In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, p. 221-240Article, review/survey (Refereed)
    Abstract [en]

    This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

  • 32.
    Leijon, Mats
    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.
    Lejerskog, Erik
    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.
    A wave power unit2009Patent (Other (popular science, discussion, etc.))
  • 33.
    Leijon, Mats
    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.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A resonance circuit for electrical conversion systems2011In: PS Public Service Review, Vol. European Union, no 22, p. 268-271Article in journal (Refereed)
  • 34.
    Leijon, Mats
    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.
    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.
    Boström, Cecilia
    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.
    Tyrberg, Simon
    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.
    Gravråkmo, Halvar
    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.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    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.
    Danielsson, Oskar
    Eriksson, Mikael
    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.
    Bolund, Björn
    Gustafsson, Stefan
    Thorburn, Karin
    Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach2009In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed)
    Abstract [en]

    The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

  • 35.
    Lejerskog, Erik
    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.
    Hai, Ling
    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 on power absorption from a wave energy converter at the Lysekil wave energy research site2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 77, p. 9-14Article in journal (Refereed)
    Abstract [en]

    Power generation from wave power has a large potential to contribute to our electric energy production, and today, many wave power projects are close to be commercialized. However, one key issue to solve for many projects is to decrease the cost per installed kW. One way to do this is to investigate which parameters that have a significant impact on the wave energy converters (WEC) performance. In this paper, experimental results on power absorption from a directly driven point absorbing WEC are presented. The experiments have been carried out at the Lysekil research site in Sweden. To investigate the performance of the WEC, the absorbed power and the speed of the translator are compared. The result confirms that the buoy size and the translator weight have a large impact on the power absorption from the generator. By optimizing the buoy size and translator weight, the WEC is believed to produce power more evenly over the upward and downward cycle. Moreover, to predict the maximum power limit during normal operation, a simulation model has been derived. The results correlates well with experimental data during normal operation. 

  • 36.
    Lejerskog, Erik
    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.
    Savin, Andreij
    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.
    Tyrberg, Simon
    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.
    Krishna, Remya
    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.
    Ekström, Rickard
    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.
    Engström, Jens
    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.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kurupath, Venugopalan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hai, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    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.
    Lysekil Research Site, Sweden: A status update2011In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper (Refereed)
  • 37.
    Lundin, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goncalves de Oliveira, Janaina
    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.
    Yuen, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjeilin, Jon
    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.
    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.
    Dynamic stability of an electricity generation system based on renewable energy2011In: Proceedings of CIRED 2011 - the 21st International Conference and Exhibition on Electricity Distribution, CIRED - Congrès International des Réseaux Electriques de Distribution, 2011, p. 0940-Conference paper (Refereed)
    Abstract [en]

    Renewable energy must be stored in order to make itreliable. Flywheels are capable of storing high amounts ofenergy and can also be used as power buffers, due to theirhigh power densities. This paper investigates a way tosmooth the power output from renewable energy converters(wave, wind and marine current) by adding a doublewoundflywheel energy storage to the system. Simulationsshow that a ramp-controlled flywheel energy storage woulddrastically smooth the short time power from a wave energyconverter but not be that appropriate for longer termenergy storage. The power quality enhancement producedby the addition of the flywheel to the system is alsosimulated and discussed.

  • 38.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Almeida, Pedro
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    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.
    A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control ApplicationIn: International Marine Energy Journal, ISSN 2631-5548Article in journal (Refereed)
    Abstract [en]

    The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.

  • 39.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cardosa Silva, Dalmo
    Department of Electrical Engineering, Universidade Federal de Juiz de Fora, Juiz de Fora, Brazil.
    Potapenko, Tatiana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hjalmarsson, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kelly, James
    MaREI―Centre for Marine and Renewable Energy Ireland, University College Cork, Cork, Ireland.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goncalves de Oliveira, Janaína
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Department of Electrical Engineering, Universidade Federal de Juiz de Fora, Juiz de Fora, Brazil.
    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. Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids2019In: Energy and Power Engineering, ISSN 1949-243X, E-ISSN 1947-3818, Vol. 11, no 3, p. 99-131Article in journal (Refereed)
    Abstract [en]

    Renewable energy sources, such as photovoltaicwind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous ge-nerators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is imple-mented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed con-troller uses a current synchronous detection scheme to emulate a virtual iner-tia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power manage-ment control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.

  • 40.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chatzigiannakou, Maria A.
    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.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    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.
    Grid Integration and a Power Quality Assessment of a Wave Energy Park2019In: IET Smart Grid, ISSN 2515-2947, p. 1-14Article in journal (Refereed)
    Abstract [en]

    This paper presents a step towards the grid connection of a wave energy park through an electric power conversion system(EPCS)developed and installed for the wave energy harvesting in Lysekil, Sweden.TheEPCScomprises ofa rectifier,aDC-bus,andan inverterfollowedbyaharmonic filter. The higher and lowerorder harmonics injected bythe inverterin a power quality contextare investigated. The lowerorder voltage harmonics partially distort the voltage sourceinverter(VSI)outputgridcurrent.Aphase-lockedloop(PLL)basedgridphasetrackingisusedtoattenuatethelowerorder harmonicsbyreflectingthegridharmonicsintheinverteroutput.Anexpressionforthegridcurrentharmonicsasafunctionofthe gridvoltageharmonicshasbeenderived and implemented. AmathematicalmodelisderivedtoobtainatransferfunctionforthePLLand finally,PI-gainsaretunedforastablesystemoperation.Aharmonicfilterfor mitigatingthehigherorderharmonicshas beenimplemented. The total harmonic distortion (THD) is evaluated experimentally and theresults fulfill the gridcoderequirementsat various frequencies and harmonic orders.

  • 41.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chatzigiannakou, Maria A.
    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.
    Temiz, Irina
    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.
    Oliveira, Janaína Goncalves de
    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 Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System2018Conference paper (Refereed)
  • 42.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chatzigiannakou, Maria
    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.
    Temiz, Irina
    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.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Fed Juiz De Fora, Juiz De Fora, Brazil.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Chalmers Univ Technol, Dept Elect Engn, Gothenburg, Sweden.
    Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System2018In: 2018 5TH INTERNATIONAL CONFERENCE ON ELECTRIC POWER AND ENERGY CONVERSION SYSTEMS (EPECS)., 2018Conference paper (Refereed)
    Abstract [en]

    This paper provides an overview of electric power conversion system installed at the Lysekil research site, located at the west coast of Sweden. The electric power conversion system consists of rectifiers, rectifying the power from the wave energy converters, a DC-link and a grid-tied inverter. The paper focuses on the performance of the inverter and the filter and presents experimental results obtained during the grid integration.

  • 43.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universidade Federal de Juiz de Fora, Brazil.
    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. Chalmers University of Technology.
    Energy management for a grid-connected wave energy park through a hybrid energy storage system2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 231, p. 399-411Article in journal (Refereed)
    Abstract [en]

    The concern for climate change and energy consumption has increased the demand for renewable energy production considerably. Marine energy sources attract attention because of their high energy density. Wave energy is an attractive renewable energy source with large potential. Due to the nature of the ocean waves, a linear wave energy converter generates intermittent power. It is therefore crucial to regularize the power before connecting to the grid. Energy storage systems present effective ways to minimize the power fluctuations and deliver a steady power to the grid. In this paper, we present an energy management control system with a dynamic rate limiter. The method is applied to control a hybrid energy storage system, combining battery and supercapacitor, with a fully active topology controlled by the power converters. The results show that the method is able to control the charging and discharging states of the battery and the supercapacitor, and minimize the power fluctuation to the grid. The algorithm ensures low losses by shifting the required power and the stored power smoothly over the energy storage system.

  • 44.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Hjalmarsson, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Potapenko, Tatiana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Anttila, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kelly, James
    Temiz, Irina
    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.
    Grid Impact and Power quality Assessment in wave Energy Parks: Different layouts and Power Penetrations using Energy StorageIn: IET Electric Power Applications, ISSN 1751-8660, E-ISSN 1751-8679, ISSN 1751-8679Article in journal (Refereed)
  • 45.
    Potapenko, Tatiana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Parwal, Arvind
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kelly, James
    Hjalmarsson, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Anttila, Sara
    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.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power Hardware in-the-Loop Real Time Modelling using Hydrodynamic Model of a Wave Energy Converter with Linear generator Power Take-Off2019In: the 29th International Ocean and Polar Engineering Conference (ISOPE), Honolulu, Hawaii, USA, June 16-21, 2019, 2019Conference paper (Refereed)
  • 46.
    Rahm, Magnus
    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.
    Svensson, Olle
    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.
    Bülow, Fredrik
    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.
    Laboratory experimental verification of a marine substation2009In: The 8th European Wave and Tidal Energy Conference EWTEC 2009: book of abstracts, Uppsala, 2009, p. 51-58Conference paper (Refereed)
  • 47.
    Rahm, Magnus
    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.
    Svensson, Olle
    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.
    Bülow, Fredrik
    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 underwater substation for wave energy converter arrays2010In: IET Renewable Power Generation, ISSN 1752-1416, Vol. 4, no 6, p. 602-612Article in journal (Refereed)
    Abstract [en]

    In this study, the design, construction, deployment and operation of an offshore underwater substation is discussed. The seabed placed substation interconnects three linear generator wave energy converters (WECs) at the Swedish Lysekil wave energy research site. The power from the WECs fluctuates because of their direct-driven topology. The generator voltage has varying electrical frequency and amplitude. To reduce the fluctuations, the individual voltages of the WECs are rectified and the power is added on a common DC-bus in the substation. The voltage is inverted, transformed and power is transmitted to an on-shore resistive load. The substation was retrieved on two occasions since the deployment in the spring of 2009. The functionality of the substation is validated by comparing voltage and current wave forms from Simulink with measured results from laboratory experiments. In addition, a sample of results from real offshore operation is illustrated and discussed. With a proportional-integral-derivative (PID)-regulator in the inverter control, the small fluctuations in the DC-bus voltage could be minimised. However, this would reduce the energy storage capability of the DC-link smoothing capacitors.

  • 48.
    Rahm, Magnus
    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.
    Boström, Cecilia
    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 the operation of aggregated wave energy converters2012In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 6, no 3, p. 149-160Article in journal (Refereed)
    Abstract [en]

    Wave energy comes in pulses and is unsuitable for direct conversion and transmission to the grid. One method to smooth the power is to deploy arrays of wave energy converters (WECs), the geometrical layout and damping optimisation of which many have studied analytically and numerically, but very few by experiments at sea. In this study, the standard deviation of electrical power as function of various parameters is investigated. Two offshore experiments have been conducted. During the longer run, three WECs were operated in linear damping during 19.7 days. It is shown that the standard deviation reduces with the number of WECs in the array up to three WECs. The reduction compared to single WEC operation was found here to be 30 and 80% with two and three WECs, respectively, as a mean for an arbitrary array member. It is found that in sea states above ~2 kW/m, the standard deviation is independent of sea state parameters. This is contradictory to a previous study on the same device. The results are, however, in accordance with numerical results of the SEAREV device but show larger reduction in standard deviation with number of WECs. This could be because of suboptimal damping conditions.

  • 49.
    Savin, Andrej
    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.
    Strömstedt, Erland
    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.
    Determining the service life of a steel wire under a working load in the Wave Energy Converter (WEC)2009Conference paper (Refereed)
  • 50.
    Silva Junior, Dalmo C.
    et al.
    Univ Fed Juiz de Fora, Elect Engn Program, Multiplatform Simulat Lab, Juiz De Fora, MG, Brazil.
    Oliveira, Janaína Goncalves de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Fed Juiz de Fora, Elect Engn Program, Multiplatform Simulat Lab, Juiz De Fora, MG, Brazil.
    de Almeida, Pedro M.
    Univ Fed Juiz de Fora, Elect Engn Program, Multiplatform Simulat Lab, Juiz De Fora, MG, Brazil.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Control of a multi-functional inverter in an AC microgrid - Real-time simulation with control hardware in the loop2019In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 172, p. 201-212Article in journal (Refereed)
    Abstract [en]

    This paper proposes the implementation of a multi-functional inverter, which was simulated with three ancillary functions. The first function is a Shunt Active Power Filter (SAPF) for harmonic content mitigation, the second is a Virtual Synchronous Machine (VSM) to show the effective regulation of voltage and frequency, and finally, power management in AC microgrids. The multi-functional converter is responsible for the integration of a PV-Battery system (distributed generation) on the AC grid. Furthermore, Real Time Digital Simulator (RTDS) and dSPACE have been used to analyze the performance and control of such multi-functional inverter when added to an AC microgrid. Results demonstrate the operation of the system and can be used as validation of the proposed control strategies through a Hardware In the Loop (HIL) simulation.

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