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A Study of the Possible Power Extraction from a Point Absorbing Wave Energy Converter
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave power)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Today there exist several different ongoing wave power projects around the world. One of them is carried out by researchers at Uppsala University, Sweden. The concept is based on a point absorbing wave energy converter (WEC). A buoy is placed on the ocean surface and connected to a direct driven linear generator placed on the seabed. When the buoy moves with the waves, the moving part of the generator will move and a voltage is induced in the stator windings. The speed of the moving part will vary between zero and a peak value twice every wave period. The maximum speed and also the power depend on the wave height, the wave length and the damping of the generator. Moreover, the maximum speed of the real sea wave will be different for every wave period. Thus, the electrical system must be designed to handle the peak power that the generator generates even though the average power is significantly lower. This paper aims to investigate the difference between the peak power and mean power further. An analytical investigation of the possible maximum and mean power extraction of the WEC is performed. A comparison and discussion between the analytical results and results from experiments are presented. Moreover, the ongoing research activities at the university's research site are presented


Keyword [en]
wave power; point absorber; linear generator, wave energy converter.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science
URN: urn:nbn:se:uu:diva-179103OAI: oai:DiVA.org:uu-179103DiVA: diva2:543406
The Lysekil Project
Available from: 2012-08-07 Created: 2012-08-07 Last updated: 2012-09-07
In thesis
1. Experimental results from the Lysekil Wave Power Research Site
Open this publication in new window or tab >>Experimental results from the Lysekil Wave Power Research Site
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source.

The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state.

The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land.

Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis.

The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter.

Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line.

Abstract [sv]

Den här avhandlingen berättar om hur experimenten vid Lysekils forskningsområde för vågkraft har utförts. Insamlade mätdata har använts för att verifiera teoretiska samband som modulerats vid Elektricitetslära, Uppsala universitet. De teoretiska och praktiska resultaten har visat på att vågkraft har förutsättningarna att implementeras som en hållbar framtida energikälla. Intressanta mätmetoder har utvecklas och påfrestningarna  på utrustningin och dess samband med medel effekten har studerats.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 101 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 957
Wave power, Lysekil, Marine Substation, Offshore measurement, strain gauge, lateral force, Invlination and azimuth angles, Wave energy converter, Temperature measurements, Inverter, Energy, Control sustem, CompactRIO, Vågkraft, Mätteknik, Styrsystem, Lysekil
National Category
Marine Engineering Energy Systems Other Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering Control Engineering
Research subject
Engineering Science
urn:nbn:se:uu:diva-179098 (URN)978-91-554-8433-0 (ISBN)
Public defence
2012-09-28, Polhem Å 10134, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Lysekils projektet
Swedish Research Council, grant no. 621-2009-3417
Available from: 2012-09-05 Created: 2012-08-07 Last updated: 2013-01-22

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