| 1. |
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| 2. |
- Boström, Cecilia, et al.
(författare)
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Design proposal of electrical system for linear generator wave power plants
- 2009
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Ingår i: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS. - : IEEE. - 9781424446483 - 9781424446506 ; , s. 4180-4185
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Boström, Cecilia, et al.
(författare)
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Study of aWave Energy Converter Connected to a Nonlinear Load
- 2009
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Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 34:2, s. 123-127
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Boström, Cecilia, et al.
(författare)
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Temperature measurements in a linear generator and marine substation for wave power
- 2010
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Ingår i: PROCEEDINGS OF THE ASME 29TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING 2010, VOL 3. - 9780791849118 ; , s. 545-552
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Boström, Cecilia, et al.
(författare)
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Temperature measurements in a linear generator and marine substation for wave power
- 2012
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Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : ASME International. - 0892-7219 .- 1528-896X. ; 134:2, s. 021901-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
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| 7. |
- Castellucci, Valeria, et al.
(författare)
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Sea level variability in the Swedish Exclusive Economic Zone and adjacent seawaters : influence on a point absorbing wave energy converter
- 2019
-
Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 15, s. 1517-1529
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Tidskriftsartikel (refereegranskat)abstract
- Low-frequency sea level variability can be a critical factor for several wave energy converter (WEC) systems, for instance, linear systems with a limited stroke length. Consequently, when investigating suitable areas for deployment of those WEC systems, sea level variability should be taken into account. In order to facilitate wave energy developers finding the most suitable areas for wave energy park installations, this paper describes a study that gives them additional information by exploring the annual and monthly variability of the sea level in the Baltic Sea and adjacent seawaters, with a focus on the Swedish Exclusive Economic Zone. Overall, 10 years of reanalysis data from the Copernicus project have been used to conduct this investigation. The results are presented by means of maps showing the maximum range and the standard deviation of the sea level with a horizontal spatial resolution of about 1 km. A case study illustrates how the results can be used by the WEC developers to limit the energy absorption loss of their devices due to sea level variation. Depending on the WEC technology one wants to examine, the results lead to different conclusions. For the Uppsala point absorber L12 and the sea state considered in the case study, the most suitable sites where to deploy WEC parks from a sea level variation viewpoint are found in the Gotland basins and in the Bothnian Sea, where the energy loss due to sea level variations is negligible.
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| 8. |
- Engström, Jens, et al.
(författare)
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Energy absorption from parks of point-absorbing wave energy converters in the Swedish exclusive economic zone
- 2020
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Ingår i: Energy Science & Engineering. - : John Wiley & Sons. - 2050-0505. ; 8:1, s. 38-49
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Tidskriftsartikel (refereegranskat)abstract
- In a future energy system based on renewable energy sources, wave energy will most likely play a role due to its high energy potential and low intermittency. The power production from parks of wave energy converters of point absorber type has been extensively studied. This is also the case for the wave energy resource at many coastal areas around the globe. Wave energy has not yet reached a commercial level, and a large variety of technologies exist; therefore, an established method to calculate the technical potential for wave energy has still not been established. To estimate the technical potential of wave energy conversion, some approximations inevitably need to be taken due to the systems high complexity. In this study, a detailed mapping of the wave climate and simulation of large arrays of hydrodynamically cross‐coupled wave energy converters are combined to calculate the technical potential for wave energy conversion in the Swedish exclusive economic zone. A 16‐year wave data set distributed in a 1.1 km × 1.1 km grid is used to calculate the absorbed energy from a park of 200 generic point absorbers. The areas with best potential have an average annual energy absorption of 16 GWh for the selected wave energy park adapted to 1 km2 when using a constant damping, while the theoretical upper bound is 63 GWh for the same area.
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| 9. |
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| 10. |
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| 11. |
- Gravråkmo, Halvar, et al.
(författare)
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Measurements of Extreme Forces on a Wave Energy Converter of Point Absorber Type and Estimation of Added Mass of Cylindrical Buoy
- 2014
-
Ingår i: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9B. - : ASME Press. - 9780791845547
-
Konferensbidrag (refereegranskat)abstract
- A wave energy converter (WEC) of point absorber type is tested at the west coast of Sweden. The buoy is a vertical cylinder. The linear generator on the seabed has limited stroke length. Large waves cause the generator to reach its maximum stroke length. As this happen, a spring in the generator is compressed, causing the buoy to instantly come to rest. During this process the force between the buoy and the generator is measured. Also the acceleration of the buoy is measured. This process and the extreme forces on the generator hull is described and the study shows that the magnitude of this force is greatly influenced by the added mass of the buoy and thus the buoy geometry. The ratio between the extreme forces on the hull and the forces during normal operation will affect the dimensioning and economy of the WEC. Force acting between generator and buoy were measured during various events as the WEC was operating. Added mass was estimated from the measurements
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| 12. |
- Gravråkmo, Halvar, et al.
(författare)
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Power Production by Linear Wave Energy Converters of Point Absorber Type with Vertical Cylindrical Buoys during Various Sea States
-
Tidskriftsartikel (refereegranskat)abstract
- Two wave energy converters (WEC) were deployed near the city of Lysekil as part of Uppsala University's wave energy project. The converters were electrically identical and mechanically very similar. The converters were installed on the seabed at 25 m depth at the same site and believed to be exposed to very similar wave conditions. They utilized permanent magnets oscillating vertically due to surface buoys actuating the generators. The buoys were vertical cylinders excitated by ocean waves, with different diameters but with equal volume. The power production from the converters and the sea states were measured and comparison of power production between the two converters during various sea states was conducted. Also wind and tidal oscillations were considered and were found to influence the power production directly or indirectly, as did also significant wave height and energy period. The only difference between the two converters were the buoys, as the generators and electric loads were equal. During a 4 day period of various wave climates, the WEC with the buoy with 78 % larger water plane area than the WEC with the more narrow buoy with a water plane area of 7.07 m2 was found to produce 11 % more power.
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| 13. |
- Gravråkmo, Halvar, et al.
(författare)
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Toroidal Buoy for Point Absorver WEC with Focus on Added Mass and Overloads
-
Tidskriftsartikel (refereegranskat)abstract
- In order for a wave energy converter (WEC) to produce electricity at competitive prices, the generator must not be over dimensioned in order to save money on production, transport and installation, but the WEC, in this case a point absorber, must also be dimensioned to withstand harsh sea states. High added mass will in some cases create severe inertia forces on the generator and might shorten the service life of the system. The magnitude of the overload forces can be reduced by choosing a buoy geometry with small added mass. Measurements of snap loads produced by a toroidal buoy and calculations of buoy intertia forces causing overloads on a generator with a toroidal buoy and an equal generator with a cylindrical buoy are investigated in order to compare the two shapes numerically. A toroidal buoy was found to have less added mass than a vertical cylindrical buoy with similar excitation force, which caused reduced overloads at short wave periods, thus reducing the overloads on the generator. Snap loads were found to not cause much greater loads than other forces found during operation.
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| 14. |
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| 15. |
- Jonsson, Anthon, 1993-, et al.
(författare)
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Test rig for submerged transmissions in wave energy converters as a development tool for dynamic sealing systems
- 2023
-
Ingår i: Proceedings of the 15th European Wave and Tidal Energy Conference (EWTEC 2023), Bilbao, 3-7 September, 2023.
-
Konferensbidrag (refereegranskat)abstract
- A submerged transmission, fitted with a dynamic sealing system, in a wave energy converter (WEC) serves the purpose of transmitting the force, absorbed by a wave activated body, to an encapsulated power take-off (PTO) system, while preventing seawater from entering the capsule. Dry generator operation is generally a prerequisite for attaining long technical service life. Little attention seems to be devoted in publications to the study of dynamic sealing systems in WECs, and to test rigs for experimental verification and/or evaluation of the ability/performance of existing dynamic sealing systems in a controlled laboratory environment. This paper begins by presenting some of our earlier research within the focus area of dynamic sealing systems, incl. design considerations and typical operating conditions. This part also presents the 1st laboratory test rig, used for verifying the sealing ability of the piston rod mechanical lead-through design in the 1st and 2nd full-scale experimental WEC prototype from Uppsala University. In 2021 project DynSSWE (Dynamic Sealing Systems for Wave Energy) was initiated. Drawing from experience, the project includes development of a new test rig, representing a tool for further development of dynamic sealing systems. This paper introduces steps in the design and development process of that new test rig, enabling accelerated long-term test runs with a setup of multiple piston rod specimens. The test specimens’ will be surface treated differently with the aim of improving the prospects of a long maintenance free service life. Since the new test rig is in the design stage, seal testing results are not yet reported. The presented work is funded by the Swedish energy agency with the aim of improving subsystem performance in wave energy devices.
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| 16. |
- Leijon, Mats, 1958-, et al.
(författare)
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A wave power unit, a buoy, use of a wave power unit and a method for producing electric energy
- 2008
-
Patent (populärvet., debatt m.m.)abstract
- The invention relates to a wave power unit with a buoy, adapted to float on a water surface. An electric generator is connected to the buoy through connection means. According to the invention the buoy when floating on a water surface and when seen in a direction perpendicular to the water surface has the shape of a closed loop enclosing an inner opening. The invention also relates to a buoy for a wave power unit, which buoy has the corresponding features as above. Further, the invention relates to the use of the invented wave power unit and to a method for producing electric energy with the invented wave power unit.
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| 17. |
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| 18. |
- Leijon, Mats, et al.
(författare)
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Wave Energy from the North Sea : Experiences from the Lysekil Research Site
- 2008
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Ingår i: Surveys in geophysics. - : Springer Science and Business Media LLC. - 0169-3298 .- 1573-0956. ; 29:3, s. 221-240
-
Forskningsöversikt (refereegranskat)abstract
- 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.
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| 19. |
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| 20. |
- Lejerskog, Erik, 1977-, et al.
(författare)
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Study of the operation characteristics of a point absorbing direct driven permanent magnet linear generator deployed in the Baltic Sea
- 2016
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 10:8, s. 1204-1210
-
Tidskriftsartikel (refereegranskat)abstract
- To experimentally study how a wave energy converter (WEC) behaves when parameters such as weight on the translator and buoy volume are changing is of significant importance when trying to optimise the WEC system. This study presents results from a WEC deployed at the Baltic Sea near the island of Åland. Compared with earlier experiments, the weight on the translator has been significantly increased to suit the buoy volume. Experimental results show that the power output between the upward and the downward motions are comparable up to the maximum speed for the downward motion of the translator. To study the speed of the translator in downward direction a model has been derived. The model has also been used to study the impact of having a changing active area. Moreover, finite element (FE) simulations done on the generator have been compared with experimental data and show a good agreement, but at high speeds of the translator the FE simulations start to deviate from the experiments.
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| 21. |
- Nilsson, Erik, 1983-, et al.
(författare)
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Assessment of Extreme and Metocean Conditions in the Swedish Exclusive Economic Zone for Wave Energy
- 2020
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 11:3
-
Tidskriftsartikel (refereegranskat)abstract
- Here, accessibility to near-shore and offshore marine sites is evaluated based on wave and ice conditions. High-resolution third-generation wave model results are used to examine the operation and maintenance conditions for renewable energy sources with a focus on wave energy. Special focus is given to the wave field and ice characteristics for areas within the Swedish Exclusive Economic Zone including analysis of return levels for extreme values for significant wave height, which provides guidance for dimensioning wave energy converters. It is shown that the number of weather windows and accessibility are influenced by distance from the coast and sea-ice conditions. The longest waiting periods for the closest weather window that is available for Operation and Maintenance (O&M) is in ice-free conditions shown to be strongly correlated with the fetch conditions. The sheltered Baltic Sea is shown to have very high accessibility if marine infrastructure and vessels are designed for access limits of significant wave height up to 3 m. In the northern basins, the waiting periods increase significantly, if and when the ice-conditions are found to be critical for the O&M activity considered. The ice-conditions are examined based on compiled operational sea-ice data over a climatic time period of 34 years. The results are location specific for the Swedish Exclusive Economic Zone, but the analysis methods are transferable and applicable to many other parts of the world, to facilitate assessment of the most promising areas in different regions.
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| 22. |
- Nilsson, Erik O., 1983-, et al.
(författare)
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Characterization of Wave Energy Potential for the Baltic Sea with Focus on the Swedish Exclusive Economic Zone
- 2019
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 12:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, a third-generation wave model is used to examine the wave power resource for the Baltic Sea region at an unprecedented one-kilometer-scale resolution for the years 1998 to 2013. Special focus is given to the evaluation and description of wave field characteristics for the Swedish Exclusive Economic Zone (SEEZ). It is carried out to provide a more detailed assessment of the potential of waves as a renewable energy resource for the region. The wave energy potential is largely controlled by the distance from the coast and the fetch associated with the prevailing dominant wave direction. The ice cover is also shown to significantly influence the wave power resource, especially in the most northern basins of the SEEZ. For the areas in focus here, the potential annual average wave energy flux reaches 45 MWh/m/year in the two sub-basins with the highest wave energies, but local variations are up to 65 MWh/m/year. The assessment provides the basis for a further detailed identification of potential sites for wave energy converters. An outlook is given for additional aspects studied within a broad multi-disciplinary project to assess the conditions for offshore wave energy conversion within the SEEZ.
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| 23. |
- Nyberg, Johan, et al.
(författare)
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Spatial characterization of seabed environmental conditions and geotechnical properties for the development of marine renewable energy in Sweden
- 2022
-
Ingår i: Quarterly journal of engineering geology and hydrogeology. - : Geological Society of London. - 1470-9236 .- 2041-4803. ; 55:4, s. 1-23
-
Tidskriftsartikel (refereegranskat)abstract
- Although knowledge of seabed properties is of high importance in selecting sites and determining technical designs and solutions for renewable energy offshore installations, it is often overlooked in marine spatial planning, owing to the absence of appropriate spatial analysis of these conditions. Identification and quantification of seabed conditions and geotechnical properties in finding safe and environmentally sustainable areas for installations of offshore renewable energy are therefore presented, using information produced in marine geological mapping. Six seabed environmental and 13 geotechnical parameters, which can be extracted from existing marine geological information and are of importance in analysing environmental conditions and planning designs are identified and presented, in addition to the suitability of various installation techniques for different areas on the Swedish seabed. Geographical information systems (GIS) are used to geo spatially evaluate the different parameters in finding suitable locations and cable routes for a wave energy plant with gravity and/or suction caisson foundations. The presented categories and ranges of the environmental and geotechnical values for the various parameters have the possibility to be improved as new data are produced from future mapping. The parameters identified and presented here are valuable as they can be incorporated into multi-parameter evaluations for optimal site selection of different offshore installations.
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| 24. |
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| 25. |
- Parwal, Arvind, et al.
(författare)
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Grid integration and a power quality assessment of a wave-energy park
- 2019
-
Ingår i: IET Smart Grid. - UK : Institution of Engineering and Technology (IET). - 2515-2947. ; 2:4, s. 625-634
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a step toward 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. The EPCS comprises a rectifier, a DC bus, and an inverter followed by a harmonic filter (HF). The higher- and lower-order harmonics injected by the inverter in a power quality context are investigated. The lower-order voltage harmonics partially distort the voltage-source inverter output grid current. A phase-locked loop-based (PLL) grid-phase tracking is used to attenuate the lower-order harmonics by reflecting the grid harmonics in the inverter output. An expression for the grid-current harmonics as a function of the grid-voltage harmonics has been derived and implemented. A mathematical model is derived to obtain a transfer function for the PLL, and finally, proportional–integral gains are tuned for stable system operation. An HF for mitigating the higher-order harmonics has been implemented. The total harmonic distortion is evaluated experimentally, and the results fulfil the grid-code requirements at various frequencies and harmonic orders.
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| 26. |
- Parwal, Arvind, et al.
(författare)
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Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden : A Status Update
- 2015
-
Konferensbidrag (refereegranskat)abstract
- This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.
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| 27. |
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| 28. |
- Savin, Andrej, et al.
(författare)
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Full-Scale Measurement of Reaction Force Caused by Level Ice Interaction on a Buoy Connected to a Wave Energy Converter
- 2019
-
Ingår i: Journal of cold regions engineering. - : ASCE-AMER SOC CIVIL ENGINEERS. - 0887-381X .- 1943-5495. ; 33:2
-
Tidskriftsartikel (refereegranskat)abstract
- Wave energy is an attractive source of renewable energy. In regions with a cold climate, for example, in the Baltic Sea, a good understanding of ice loads is vital for developing a reliable and cost-effective buoy for a wave energy converter (WEC). The first full-scale attempt was made to measure the vertical reaction force on a floating buoy connected to the WEC under the ice level interaction process. The force equation for a buoy connected to the WEC during the ice level interaction process is presented. It provides essential information on forces from the floating level of ice, which is very important for the design and construction of a buoy in regions with a cold climate.
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| 29. |
- Savin, Andrej, et al.
(författare)
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Statistical analysis of power output from a single heaving buoy WEC for different sea states
- 2018
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Ingår i: Marine Systems & Ocean Technology. - : Springer. - 1679-396X .- 2199-4749. ; 2-4, s. 103-110
-
Tidskriftsartikel (refereegranskat)abstract
- Output power fluctuations from a wave energy converter (WEC) utilizing the principle of an oscillating body are unavoidable due to the reciprocating movement of the translator inside the generator. Moreover, the wave energy flux largely varies with time and propagates with the wave group velocity. Making use of the oscillating output power is a challenge for many wave energy conversion concepts. Therefore, estimation of the output power from a WEC solely by the mean power does not fully reflect the process of energy conversion, especially, by a direct drive linear generator. In the present paper, the output power from the WEC with a linear generator power take-off (PTO) is considered as a stochastic process, and the WEC performance is evaluated from the statistical point of view and related to the linear generator’s (LG) stroke length. Statistics as mean, standard deviation, relative standard deviation, maximum, and mode are found for different sea states. All statistics have shown an expected overall tendency with a rising significant wave height of incoming waves. As the significant wave height increases, statistics of the power output such as mean, standard deviation, maximum, and quantile are increasing, and the mode is decreasing beside the mode for the sea state C. It has been noted that for a significant wave height equal to the LG’s stroke length, the mode is greater than the same values for sea states of other significant wave heights. The results are based on a full-scale offshore experiment and may be used for the design of energy conversion systems based on a linear generator PTO.
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| 30. |
- Sjökvist, Linnea, et al.
(författare)
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Calculating Buoy Response for a Wave Energy Converter - a Comparsion Between Two Computational Methods and Experimental Results
- 2017
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Ingår i: Theoretical and Applied Mechanics Letters. - : Elsevier BV. - 2095-0349. ; 7:3, s. 164-168
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Tidskriftsartikel (refereegranskat)abstract
- When designing a wave power plant, reliable and fast simulation tools are required. Computational fluid dynamics (CFD) software provides high accuracy but with a very high computational cost, and in operational, moderate sea states, linear potential flow theories may be sufficient to model the hydrodynamics. In this paper, a model is built in COMSOL Multiphysics to solve for the hydrodynamic parameters of a point-absorbing wave energy device. The results are compared with a linear model where the hydrodynamical parameters are computed using WAMIT, and to experimental results from the Lysekil research site. The agreement with experimental data is good for both numerical models.
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| 31. |
- Strömstedt, Erland, 1972-, et al.
(författare)
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A Set-Up of 7 Laser Triangulation Sensors and a Draw-Wire Sensor for Measuring Relative Displacement of a Piston Rod Mechanical Lead-Through Transmission in an Offshore Wave Energy Converter on the Ocean Floor
- 2012
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Ingår i: ISRN Renewable Energy. - New York : Hindawi Publishing Corporation. - 2090-746X. ; 2012, s. 746865-
-
Tidskriftsartikel (refereegranskat)abstract
- A concept for offshore wave energy conversion is being developed at the Swedish Centre for Renewable Electric Energy Conversion at Uppsala University in Sweden. The wave energy converter (WEC) in focus contains a piston rod mechanical lead-through transmission for transmitting the absorbed mechanical wave energy through the generator capsule wall while preventing seawater from entering the capsule. A set-up of 7 laser triangulation sensors has been installed inside the WEC to measure relative displacement of the piston rod and its corresponding seal housing. A draw-wire sensor has also been set up to measure translator position and the axial displacement of the piston rod. The paper gives a brief introduction to the Lysekil research site, the WEC concept, and the direct drive of WEC prototype L2. A model of operation for the piston rod mechanical lead-through transmission is given. The paper presents sensor choice, configuration, adaptation, mounting, and measurement system calibration along with a description of the data acquisition system. Results from 60 s measurements of nominal operation two months apart with centered moving averages are presented. Uncertainty and error estimations with statistical analyses and signal-to-noise ratios are presented. Conclusions are drawn on the relative motions of the piston rod and the seal housing under normal operating conditions, and an assessment of the applicability of the measurement system is made.
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| 32. |
- Strömstedt, Erland, 1972-, et al.
(författare)
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A wave power unit
- 2010
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Patent (populärvet., debatt m.m.)abstract
- The invention relates to a wave-power unit for the production of electric power. It comprises a floating body arranged for floating on the sea and an electric linear generator having a stator and a translator reciprocating along a center axis. The stator is arranged to be anchored in the bed of the sea and the translator is connected tothe floating body by connection means. According to the invention the generator is enclosed in a watertight encapsulation having an upper end wall with an opening through which the connection means extends. The opening has a seal that seals against the connection means. The seal is flexibly mounted. The invention also relates to the use of the wave-power unit and to a method for producing electric power.
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| 33. |
- Strömstedt, Erland, 1972-, et al.
(författare)
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In-Situ Measurements of Relative Displacement between Piston Rod and Seal Housing with Estimations of Wear on a Sealing System in a Submerged Transmission of an Offshore Underwater Wave Energy Converter
-
Ingår i: Journal of Renewable and Sustainable Energy. - 1941-7012.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A type of submerged piston rod mechanical lead-through transmission has been designed and implemented inside the two first full scale wave energy converter (WEC) prototypes at the Lysekil wave energy research site on the Swedish west cost. The transmission constitutes a direct drive which transfers the mechanical force, absorbed from the waves by a heaving surface-floating buoy, through an encapsulation and into a permanent magnet linear generator bolted to a foundation on the seabed, while sealing off the corrosive seawater. A set-up of 7 laser triangulation sensors has been installed in the second wave energy converter prototype to measure the relative displacement of the piston rod and the seal housing in-situ. This paper focus on investigating the relative tilt angles of both objects, the differential tilt angle between the piston rod and the seal housing and how they move in the time and space as they tilt with the ocean waves. Estimations on wear of the sealing components in the dynamic sealing system are made. The measurements are performed for two sea states with 2.5 month separation. The paper describes the experimental set-up and the sensor measuring systems. Equations for calculating the relative differential tilt angle between piston rod and seal housing are presented. The calculated differential tilt angle is correlated with measurements of the piston stroke length and translator position performed with the draw-wire sensor. Tilt angles, azimuth angles and differential tilt angles are presented for one wave period in each measurement period. The wear is estimated by calculating the relative change in traversed clearance gap by the piston rod across the interface inside the seal housing. Results show the expected differential tilt angle early in the experiment. A substantial increase in differential tilt angle developed over 3 months time as a consequence of large wear between buoy line and guiding funnel causing a large tilt angle on the piston rod and unintentionally large normal forces between piston rod and the dynamic sealing system inside the seal housing. The results indicate the need of a more flexible mechanical lead-through design, which is presented at the end of the paper. The results are discussed and conclusions are drawn with specific emphasis on improving the sealing system with stronger guide elements and the patented mechanical lead-through design.
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| 34. |
- Strömstedt, Erland, 1972-, et al.
(författare)
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Measurements of Relative Displacement and Tilting of a Piston Rod Transmission in a Submerged Linear Wave Energy Converter Operating with End Stop Impact
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Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - 0892-7219 .- 1528-896X.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A type of piston rod mechanical-lead through transmission has been designed and implemented inside the two first wave energy converter (WEC) prototypes at the Lysekil wave energy research site on the Swedish west cost. The transmission constitutes a direct drive which transfers the mechanical force, absorbed from the waves by a heaving surface-floating buoy, through an encapsulation and into a permanent magnet linear generator bolted to a foundation on the seabed, while sealing off the corrosive seawater. A set-up of 7 laser triangulation sensors have been installed in the second wave energy converter prototype to measure the relative displacement of the piston rod and seal housing in the mechanical lead-through in-situ. This paper presents measurements from full scale operation in two different sea states with end stop impact. Since wear is a successive process stretched out over time measurements have been performed for both sea states with 2.5 month separation. The experimental set-up and sensors are described. Equations for calculating tilt angles and azimuth angles for the piston rod are presented. Results from structure mechanical FEM simulations performed on the wave energy converter structure at end stop impact is also presented. The laser sensor measurements of the relative sideway displacements are correlated with measurements of the translator position and piston rod stroke length performed with a draw wire sensor. A force transducer is used for measuring the force in the buoy line to better understand the variations in motion due to changes in the buoy line axial force. Tilt angles and azimuth angles are presented for a wave period in each measurement period. The results are discussed and conclusions drawn with specific emphasis on the effects of the end stop impacts and wear on the funnel. The successive wear in the buoy line guiding system results in a 6 fold increase in relative tilt angle of the piston rod over a period of 2.5 months. A corresponding increase in motion is also seen for the seal housing, but to a lesser extent, indicating wear on the dynamic sealing system housed inside. The measurements of the relative displacement of the piston rod and seal housing are intended for further research.
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| 35. |
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| 36. |
- Strömstedt, Erland, 1972-
(författare)
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Project-led PBL with a Mixed-Mode Approach for a Midterm Freshman Course in Electrical Engineering Realizing All-Electric Powertrains for Vehicles
- 2020
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Ingår i: 2020 IEEE Frontiers in Education Conference (FIE). - 9781728189611 - 9781728189628
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Konferensbidrag (refereegranskat)abstract
- This Full Paper on Innovative Practise introduces a successful pedagogical approach to active student learning and student centred teaching in a large project course in electrical engineering for 70 midterm freshmen students in two educational programs at Uppsala University. Each program is challenged with the complev electrical engineering task of realizing an all-electric powertrain from component level for a passenger car. The first two rounds of the course struggled and not until the presented approach was taken into practise were the main project objectives achieved The principles for the approach are based on project-led PM. with a so-called mixed-nude approach by adding a variety of supporting content supplied through various teaching methods and by applying adapted concurrent project management methods. The paper addresses the arguments for the approach, the course design, objectives, and some of the successful solutions over the last 6 years. The approach has been evaluated by extensive written student course evaluations, student examination results, the experiences of the team of teachers from faculty, and compared over time. It is shown how the approach effectively enables achievement of the project and learning objectives, increases subject interest, provides valuable experiences from a project work environment, and in the process inspires and motivates students towards a career in engineering, thereby increasing the retention within the education. Both students and teachers have greatly appreciated the course and it is likely that the presented approach can be used also in other similar project courses in engineering.
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| 37. |
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| 38. |
- Strömstedt, Erland, 1972-
(författare)
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Submerged Transmission in Wave Energy Converters : Full Scale In-Situ Experimental Measurements
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different wave power technologies are in development around the world in different stages of prototype testing. So far only a few devices have been deployed offshore at full scale for extended periods of time. Little data is published about how these different devices perform.This thesis presents results from experiments with the full-scale offshore wave energy converters at the Lysekil research site on the Swedish west coast. The theories, experiments, measurements, performance evaluations and developments of the submerged transmission in the direct driven permanent magnet linear generator are in focus. The reciprocating submerged transmission fulfills the purpose of transmitting the absorbed mechanical wave energy through the capsule wall into the generator, while preventing the seawater from entering the capsule and reducing the life time of the converter.A measuring system with seven laser triangulation sensors has been developed to measure small relative displacements between piston rod and seal housing in the submerged transmission with excellent accuracy for the purpose of evaluating both functional behavior and successive wear in-situ. A method for calculating relative tilt angles, azimuth angles, differential tilt angles, and successive wear in the submerged transmission has been developed. Additional sensors systems have been installed in the converter enabling correlation and a thorough investigation into the operating conditions of the transmission and the converter. The thesis presents unique results from the measurements. A data acquisition system transmits the signals from the converter on the seabed to an onshore measuring station. Results are presented in time-, frequency- and the time-frequency domain.The results have given important information for further development of the submerged transmission, which is important to the survivability of the system. The thesis describes the status of research, and is a step that may influence future designs of wave energy devices for reaching survivability and a cost-effective renewable energy system.
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| 39. |
- Strömstedt, Erland, et al.
(författare)
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Three-Dimensional Oscillation Dynamics of the In Situ Piston Rod Transmission Between Buoy Line and the Double Hinge-Connected Translator in an Offshore Linear Wave Energy Converter
- 2016
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Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : ASME International. - 0892-7219 .- 1528-896X. ; 138:3
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Tidskriftsartikel (refereegranskat)abstract
- Force and displacement measurements have been performed in situ on the piston rod mechanical lead-through transmission in the direct drive of the second experimental wave energy converter (WEC) 3 km offshore at the Lysekil research site (LRS) during a 130-day continuous full-scale experiment in 2009. The direct drive consists of a buoy line and a piston rod transmission with a double-hinged link (DHL) at the lower end connecting the point absorbing surface-floating buoy to the translator of an encapsulated permanent magnet linear generator on the seabed. The buoy line is guided by a funnel in the buoy line guiding system 3.2m above the generator capsule. The 3m long piston rod reciprocates through a mechanical lead-through in the capsule wall, sealing off seawater from entering the generator capsule. A setup of laser triangulation sensors measures the relative lateral displacement of the piston rod. This paper introduces a method and a system of equations for calculating piston rod relative tilt angle and piston rod azimuth direction of tilting from the relative lateral displacement measurements. Correlation with piston rod axial displacement and forces enables evaluation of the three-dimensional (3D) oscillation dynamics. Results are presented from 2 weeks after launch and from 3 months after launch in altogether four cases representing two different stages of wear in two different sea states. Piston rod tilting from accumulated wear in the buoy line guiding system is separated from tilting due to elastic displacement. Structural mechanical finite element method (FEM) simulations verify the magnitude of elastic displacement and indicate negligible stress and strain at the mounting point of the laser sensor setup. The proposed theory for piston rod 3D motion is validated by the experiment. As the experiment progressed, wear in the buoy line guiding system accelerated due to splitting of the buoy line jacketing compound, thereby increasing the piston rod tilt angles. Over 94 days into the experiment, 21.8mm of accumulated wear in the buoy line guiding system had altered the characteristics of the piston rod oscillations and increased the maximum piston rod relative tilt angle by 0.39 deg in the predominant azimuth direction of wave propagation. Further accumulated wear in the buoy line guiding system led to buoy line rupture 130 days after launch. The results presented in this paper have been used in assessments for improving the mechanical subsystems in subsequent experimental WECs based on the Uppsala concept.
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| 40. |
- Strömstedt, Erland, 1972-, et al.
(författare)
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Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
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Ingår i: Energy and Power Engineering. - 1949-243X.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The second wave energy converter (WEC) prototype launched at the Lysekil research site on the Swedish west coast in March 2009 contained a number of sensor systems for measuring the mechanical performance of the WEC and mechanical subsystems within the WEC. Measurements were carried out during the first experimental period starting from May 15th and ending on September 23rd. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Two measurement periods separated by 2.5 month are presented to be able to draw conclusion on what happens with time. Comparisons and correlations are made between different sensors measuring simultaneously, especially for the laser triangulation sensor measurements. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period in August. Vibrations frequencies due to wear is possible from comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.
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| 41. |
- Strömstedt, Erland, et al.
(författare)
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Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
- 2013
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Ingår i: Energy and Power Engineering. - : Scientific Research Publishing, Inc.. - 1949-243X .- 1947-3818. ; Vol.5:No.1, s. 70-91
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Tidskriftsartikel (refereegranskat)abstract
- Inside the second experimental wave energy converter (WEC) launched at the Lysekil research site on the Swedish west coast in March 2009 a number of sensor systems were installed for measuring the mechanical performance of the WEC and its mechanical subsystems. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Two measurement periods, separated by 2.5 month, are presented in this paper. One measurement is made two weeks after launch and another 3 months after launch. Comparisons and correlations are made between different sensors measuring simultaneously. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period. Vibration frequencies due to wear are recognized by comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is a sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.
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| 42. |
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| 43. |
- Thomas, Simon
(författare)
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Control of Wave Energy Converters in arrays
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One way to lower the levelized cost of energy for wave power plants and paving so the way for commercial success, is to increase the power absorption by use of advanced control algorithms. This thesis investigates the influence of the generator inertia, the generator damping and the layout on power absorption and presents a new model free strategy of controlling wave energy converters.The evaluation of all control strategies was done in a numerical simulation and in experimental 1:10 model scale wave tank tests conducted in the COAST laboratory at the University of Plymouth. The WECs used are inspired by the wave energy concept developed at Uppsala University.The influence of the generator inertia on the power absorption was tested with an uncontrolled WEC. Compared to a conventional WEC the power output could be significantly increased for small waves and high wave periods. As a simple and easy to implement control strategy, a WEC with sea state optimized generator damping was used to create a power matrix. The optimal damping factor depends on both, wave period and wave height. The power absorption increases with the wave height and when the wave period converges towards the oscillation period of the WEC.A genetic algorithm was used to obtain the optimized layouts for wave energy farms, which suggest that the converter should be placed in rows parallel to the wave front, and the position in the array has nearly no influence on the optimal control parameter.Then a collaborative learning approach using machine learning is presented, with several identical wave energy converters in a row to parallelise the search of the optimal control parameter. It was implemented to control the generator damping factor and the latching time. With the latter the power could be increased significantly.
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| 44. |
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| 45. |
- Tyrberg, Simon, 1979-, et al.
(författare)
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Wave Buoy and Translator Motions - On-Site Measurements and Simulations
- 2011
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Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 36:3, s. 377-385
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Tidskriftsartikel (refereegranskat)abstract
- For a complete understanding of a wave energy conversion device, it is important to know how the proposed device moves in the water, how this motion can be measured, and to what extent the motion can be predicted or simulated. The magnitude and character of the motion has impacts on engineering issues and optimization of control parameters, as well as the theoretical understanding of the system. This paper presents real sea measurements of buoy motion and translator motion fora wave energy system using a linear generator. Buoy motion has been measured using two different systems: a land-based optical system and a buoy-based accelerometer system. The data have been compared to simulations from a Simulink model for the entire system. The two real sea measurements of buoy motion have been found to correlate well in the vertical direction, where the measured range of motion and the standard deviation of the position distributions differed with 3 and 4 cm, respectively. The difference in the horizontal direction ismore substantial. The main reason for this is that the buoy rotation about its axis of symmetry was not measured. However, used together the two systems give a good understanding of buoy motion. In a first comparison, the simulations show good agreement with the measured motion for both translator and buoy.
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| 46. |
- Waters, Rafael, et al.
(författare)
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Experimental results from sea trials of an offshore wave energy system
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:3, s. 034105-
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Tidskriftsartikel (refereegranskat)abstract
- A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and significant insights discovered. Energy absorption dependency on load as well as output voltage and power is demonstrated. It is shown that great overload capability of the directly driven linear generator is critical, and indicated that, for resistive loads, optimal load does not vary with wave climate. Future grid supplying energy production would necessitate parks of wave power plants in order to reduce power fluctuations.
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| 47. |
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| 48. |
- Waters, Rafael, et al.
(författare)
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Ocean wave energy absorption in response to wave period and amplitude : offshore experiments on a wave energy converter
- 2011
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Ingår i: IET Renewable Power Generation. - : IEEE Press. - 1752-1416. ; 5:6, s. 465-469
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 49. |
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