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Cooling Strategies for Wave Power Conversion Systems
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Division for Electricity of Uppsala University is developing a wave power concept. The energy of the ocean waves is harvested with wave energy converters, consisting of one buoy and one linear generator. The units are connected in a submerged substation. The mechanical design is kept as simple as possible to ensure reliability.

The submerged substation includes power electronics and different types of electrical power components. Due to the high cost of maintenance operations at sea, the reliability of electrical systems for offshore renewable energy is a major issue in the pursuit of making the electricity production economically viable. Therefore, proper thermal management is essential to avoid the components being damaged by excessive temperature increases.

The chosen cooling strategy is fully passive, and includes no fans. It has been applied in the second substation prototype with curved heatsinks mounted on the inner wall of the pressurized vessel. This strategy has been evaluated with a thermal model for the completed substation. First of all, 3D-CFD models were implemented for selected components of the electrical conversion system. The results from these submodels were used to build a lumped parameter model at the system level.

The comprehensive thermal study of the substation indicates that the rated power in the present configuration is around 170 kW. The critical components were identified. The transformers and the inverters are the limiting components for high DC-voltage and low DC-voltage respectively. The DC-voltage—an important parameter in the control strategy for the WEC—was shown to have the most significant effect on the temperature limitation.

As power diodes are the first step of conversion, they are subject to large power fluctuations. Therefore, we studied thermal cycling for these components. The results indicated that the junction undergoes repeated temperature cycles, where the amplitude increased with the square root of the absorbed power.

Finally, an array of generic heat sources was optimized. We designed an experimental setup to investigate conjugate natural convection on a vertical plate with flush-mounted heat sources. The influence of the heaters distribution was evaluated for different dissipated powers. Measurements were used for validation of a CFD model. We proposed optimal distributions for up to 36 heat sources. The cooling capacity was maximized while the used area was minimized.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1454
Keywords [en]
Wave power, power conversion system, thermal management, power elctronics, passive cooling, natural convection.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:uu:diva-306706ISBN: 978-91-554-9759-0 (print)OAI: oai:DiVA.org:uu-306706DiVA, id: diva2:1049240
Public defence
2017-01-20, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageAvailable from: 2016-12-21 Created: 2016-11-02 Last updated: 2016-12-28
List of papers
1. Optimized distribution of a large number of heat sources cooled by conjugate turbulent natural convection
Open this publication in new window or tab >>Optimized distribution of a large number of heat sources cooled by conjugate turbulent natural convection
(English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606Article in journal (Refereed) Submitted
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-307944 (URN)
Available from: 2016-11-24 Created: 2016-11-23 Last updated: 2017-11-29
2. Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate
Open this publication in new window or tab >>Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate
2017 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 88, p. 234-245Article in journal (Refereed) Published
Abstract [en]

Heat source arrays are common in engineering applications. Natural convection is a reliable and silent cooling strategy. Therefore, an array of flush-mounted heat sources has been studied under conjugate conduction and natural convection condition. This studies was performed for a system with relatively large dimensions, typical for power electronics, and a modified Rayleigh number up to 2 . 10(10) A modular set of heaters was designed to vary the distribution of heat sources on the plate and investigate the influence of the spacing. Velocity and temperature were measured in the convective flow with particle image velocimetry and micro-thermocouple. The velocity field was analyzed with proper orthogonal decomposition. The first instabilities of the convective flows were described. The results gave abetter understanding of the heat transfers in these configurations and are valuable for model validation.

National Category
Energy Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:uu:diva-307943 (URN)10.1016/j.expthermflusci.2017.06.002 (DOI)000409285600023 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUp
Available from: 2016-11-24 Created: 2016-11-23 Last updated: 2017-12-01Bibliographically approved
3. Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
Open this publication in new window or tab >>Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 11, article id 912Article in journal (Refereed) Published
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.

Keywords
discrete heat sources, source array, natural convection, optimization
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-307831 (URN)10.3390/en9110912 (DOI)000388580000054 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUp
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2017-11-29Bibliographically approved
4. Assessment of Thermal Cycling in a Rectifier For WavePower Generation
Open this publication in new window or tab >>Assessment of Thermal Cycling in a Rectifier For WavePower Generation
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Natural convection allows for passive cooling which isused in many engineering applications. Placing dissipatingcomponents on a common vertical heatsink can be opti-mized to give the best possible cooling capacity. In thisstudy, a numerical model for three-dimensional conjugatedconvective and conductive heat transfer was used to evalu-ate the distribution of up to 36 ush-mounted rectangularheaters. The temperature proles and the heat uxes werecompared with experimental data for validation. The dis-sipated power was set as an input parameter and the op-timal distribution was selected as the one with the lowesttemperature elevation. Two dierent heuristicsa geo-metric parameter and an articial neural networkwereproposed and evaluated as alternatives to heavy CFD cal-culations.

National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-307945 (URN)
Conference
IET Renewable Power Generation
Available from: 2016-11-23 Created: 2016-11-23 Last updated: 2016-11-25
5. Thermal Rating of a Submerged Substation for Wave Power
Open this publication in new window or tab >>Thermal Rating of a Submerged Substation for Wave Power
2016 (English)In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 7, no 1, p. 436-445Article in journal (Refereed) Published
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.

Keywords
Computational fluid dynamics;Computational modeling;Heat transfer;Heating;Integrated circuit modeling;Substations;Wave power;Computational fluid dynamic (CFD);natural convection;ocean energy;passive cooling;power electronics;thermal management;wave power
National Category
Engineering and Technology Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-267226 (URN)10.1109/TSTE.2015.2425045 (DOI)000367340700044 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUpSwedish Energy Agency
Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2017-12-01Bibliographically approved
6. Thermal modelling of a passively cooled inverter for wave power
Open this publication in new window or tab >>Thermal modelling of a passively cooled inverter for wave power
2015 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 9, no 4, p. 389-395Article in journal (Refereed) Published
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.

Keywords
wave power plants, invertors, substations, cooling, thermal modelling, passively cooled inverter, wave power, CFD models, submerged substation, thermal contact, passive cooling
National Category
Environmental Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-252981 (URN)10.1049/iet-rpg.2014.0112 (DOI)000352809300011 ()
Available from: 2015-05-19 Created: 2015-05-18 Last updated: 2017-12-04Bibliographically approved
7. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
Open this publication in new window or tab >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
Show others...
2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

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.

Keywords
Wave energy, point absorber, experiments, arrays, generators, ROVs
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-265218 (URN)
Conference
Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2018-08-07Bibliographically approved
8. Measurement System For Wave Energy Converter - Design And Implementation
Open this publication in new window or tab >>Measurement System For Wave Energy Converter - Design And Implementation
2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, AMER SOC MECHANICAL ENGINEERS , 2014Conference paper, Published paper (Refereed)
Abstract [en]

A Wave Energy Converter (WEC) measurement system has been constructed and installed with the purpose to measure, log and evaluate the WEC's performance during operation at sea. The WEC is to be deployed at Uppsala University's wave power research site in Lysekil on the west coast of Sweden. In designing such a system the key research objectives has been (1) to study the risk of overheating due to high currents in the stator windings, (2) to evaluate how the WEC's outer structure withstands drag and bending forces from the buoy line and (3) to construct a detection system which indicates if water leaks into the generator. The measurement system was designed to collect data essential to study these key objectives. Transducers were used to measure: buoy line force, translator position, phase currents, bending and tensile strain on the generator hull, water level inside generator and the temperature at multiple places inside the generator. The measurement system has been installed and calibrated in the WEC. Furthermore, the design has been evaluated in lab experiments in order to verify the function and accuracy of the different measurements. This paper presents the underlying research objectives for developing the WEC generator measurement system, together with a description of the technical implementation.

Place, publisher, year, edition, pages
AMER SOC MECHANICAL ENGINEERS, 2014
National Category
Energy Systems Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-272118 (URN)000363499000005 ()978-0-7918-4553-0 (ISBN)
Conference
33Rd International Conference On Ocean, Offshore And Arctic Engineering
Note

Första författaren har bytt efternamn till Ulvgård

Available from: 2016-01-12 Created: 2016-01-12 Last updated: 2017-09-28
9. Status Update of the Wave Energy Research at Uppsala University
Open this publication in new window or tab >>Status Update of the Wave Energy Research at Uppsala University
Show others...
2013 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Aalborg, Denmark: , 2013
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212701 (URN)
Conference
10th European Wave and Tidal Conference (EWTEC)
Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2017-12-07
10. Temperature Study in a Marine Substation for Wave Power
Open this publication in new window or tab >>Temperature Study in a Marine Substation for Wave Power
Show others...
2012 (English)In: International Journal of Mechanic Systems Engineering, ISSN 2225-7403, Vol. 2, no 4, p. 126-131Article in journal (Refereed) Published
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-190091 (URN)
Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2017-01-18Bibliographically approved
11. Marine substation design for grid-connection of a research wave power plant on the Swedish West coast
Open this publication in new window or tab >>Marine substation design for grid-connection of a research wave power plant on the Swedish West coast
2013 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Aalborg, Denmark: , 2013
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212687 (URN)
Conference
10th European Wave and Tidal Conference (EWTEC)
Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2016-11-24
12. Lysekil Research Site, Sweden: A status update
Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
Show others...
2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-160039 (URN)
Conference
9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25

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