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  • 1.
    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.

  • 2.
    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.

  • 3.
    Castellucci, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    García-Terán, Jessica
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Industrial Engineering & Management.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Padman, Laurence
    Earth & Space Res, Corvallis, OR 97333 USA.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Influence of Sea State and Tidal Height on Wave Power Absorption2017In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 42, no 3, p. 566-573Article in journal (Refereed)
    Abstract [en]

    The wave energy converter developed at Uppsala University (Uppsala, Sweden) consists of a linear generator placed on the seabed and driven by the motion of a buoy on the water surface. The buoy is connected to the moving part of the linear generator, the translator, which is made of ferrite magnets. The translator moves vertically inducing voltage in the windings of a fixed component, the so-called stator. The energy conversion of the linear generator is affected by the sea state and by variations of mean sea level. The sea state influences the speed and the stroke length of the translator, while the variation of tidal level shifts the average position of the translator with respect to the center of the stator. The aim of this study is to evaluate the energy absorption of the wave energy converter at different locations around the world. This goal is achieved by developing a hydromechanic model which analyses the optimum generator damping factor for different wave climates and the power absorbed by the generator, given a fixed geometry of the buoy and a fixed stroke length of the translator. Economic considerations regarding the optimization of the damping factor are included within the paper. The results suggest a nominal damping factor and show the power absorption losses at various locations, each of them characterized by a different wave climate and tidal range. The power losses reach up to 67% and in many locations a tidal compensation system, included in the design of the wave energy converter, is strongly motivated.

  • 4. Das, Anup
    et al.
    Zachariah, Dave
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Comparison of two hyperparameter-free sparse signal processing methods for direction-of-arrival tracking in the HF97 ocean acoustic experiment2018In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 43, no 3, p. 725-734Article in journal (Refereed)
  • 5.
    Engström, Jens
    et al.
    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.
    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.
    Properties of the Energy Transport for Plane-Parallel Polychromatic Surface Gravity Waves in Waters of Arbitrary Depth2015In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 40, no 2, p. 408-416Article in journal (Refereed)
    Abstract [en]

    It is well known that the energy transport of ocean waves propagates with the group velocity and that the energy decreases exponentially with depth. Expanding this theory, we will derive expressions for the energy transport as a function of depth and the total instantaneous transport's development over time for waves in waters of finite depth. Solutions to the Laplace equation are found for plane-parallel polychromatic waves with linearized boundary conditions. A time series of wave elevation collected at Uppsala University's wave energy research test site is chosen to present the results. Solutions for waters of both infinite and arbitrary depths are presented and compared. The solutions are convolution-type integrals with the wave elevation where we have found efficient ways to calculate the kernels. The difference in group velocity between finite depth and infinite depth and its impact on the energy transport is clearly seen in the results. The use of the deep-water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. We further show that the total instantaneous energy transport can actually have a direction that is opposite to the direction of the waves as observed from a reference frame fixed to the seabed.

  • 6.
    Engström, Jens
    et al.
    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.
    Eriksson, Mikael
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Properties of the energy transport for plane-parallel polychromatic surface gravity waves in waters of arbitrary depthIn: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Other academic)
  • 7.
    Eriksson, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theory and Experiment on an Elastically Moored Cylindrical Buoy2006In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 31, no 4, p. 959-963Article in journal (Refereed)
    Abstract [en]

    In this paper, we compare simulated forces and accelerations for a moored floating buoy with full-scale experimental results in real ocean waves. The buoy is moored with a wire connected by springs to a concrete foundation situated at the seafloor. This study aims to develop a computer model using potential theory with a linearized free-surface boundary condition to describe the motion of such a system. The intention is to use the model for future study of wave-energy absorption and design of converters. Another objective is to see how complex a model is required to get accurate results. The method used is computationally fast and makes it possible to couple linear buoy wave interaction with nonlinear generator models, so that different loads and latching can be studied. A computationally fast method is required to model farms of wave-energy converters.

  • 8.
    Jonsson, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Lekholm, Ville
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Kratz, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Monica, Almqvist
    Dept of Measurement Technology and Industrial Electrical Engineering, Lund University.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Enclosure-Induced Interference Effects in a Miniaturized Sidescan Sonar2012In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 37, no 2, p. 236-243Article in journal (Refereed)
    Abstract [en]

    On, for instance, the miniaturized submersible explorer, Deeper Access, Deeper Understanding (DADU), only 20 cm in length and 5 cm in diameter, the sidescan sonar needs to be tightly mounted in the hull. Finite element analysis (FEA) as well as physical measurements were used to investigate the effects of beam interaction with acoustically nearby rigid boundaries. Computer simulations showed the first major dip in the beam shape to vary in strength, size, and position with the enclosure wall height, from a position of 47° at 0.0-mm wall height to 32° at 3.0-mm wall height. Hydrophonic measurements on the manufactured test device confirmed these values to within 9%, varying between 47° and 29°. In addition, Schlieren imaging was proposed and used as a noninvasive means of qualitative beam shape characterization. A field test was performed with the enclosure height set to 0 and 3 mm. With the latter height, a dark band, corresponding to a sonar sensitivity dip at about 30° in the beam, appeared in the sonar image. It was found that the beam shape is sensitive to small mounting errors, in this case where the wavelength of the sonar is on the same size scale as the enclosure. Furthermore, it was found that FEA models can be used to accurately predict enclosure effects on sonar beam shapes, and Schlieren imaging can be used to visually detect the shape deformations in mounted sonar devices.

  • 9.
    Lindblad, Liselotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kamf, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Risberg, Alexander
    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.
    Portable Data Acquisition System for Offshore Applications2019In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 44, no 3, p. 719-727Article in journal (Refereed)
    Abstract [en]

    In the development of ocean energy technologies, full-scale sea trials have proven technically challenging and expensive. As a contribution to the development of flexible, reliable, and affordable measurement systems for such sea trials, this paper presents and evaluates a portable data acquisition system. The system offers a cheap and flexible option for when and where signal infrastructure at site is not available. It is battery powered and consists of a sensor system and a logger unit. The sensor system is placed inside the object of study, which for this application is a wave power generator standing on the seafloor. The logger unit, which contains a logger with integrated data storage and a battery, is placed outside the object of study in a submersible and retrievable vessel. Sensor output is carried with 4-20-mA current signals between the sensor system and the logger, which makes the system directly compatible with a wide range of industrial sensors. For the specific setup implemented in this paper, the sensor system was used to measure voltage and current inside the generator. Beyond this, the system is designed to be adaptable for a wider range of sensors, with 16 individual signals and a sampling frequency up to 1 kHz. The custom logger is programmable and offers many options to apply different logging schedules and to limit the sensor system power supply accordingly. Evaluations show that the implemented system offers 5-22 weeks of 1-kHz and 16-bmonitoring of 16 signals, depending on a chosen logging schedule. Suggestions are also given for how to raise the operation time up to 50 weeks. The system has been tested offshore for the collection of power production data from two wave energy converters, with good results.

  • 10. Ling, Jun
    et al.
    Tan, Xing
    Yardibi, Tarik
    Li, Jian
    Lundberg Nordenvaad, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    He, Hao
    Zhao, Kexin
    On Bayesian channel estimation and FFT-based symbol detection in MIMO underwater acoustic communications2014In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 39, no 1, p. 59-73Article in journal (Refereed)
    Abstract [en]

    Reliable channel estimation and effective interference cancellation are essential for enhancing the performance of multiple-input-multiple-output (MIMO) underwater acoustic communication (UAC) systems. In this paper, an efficient user-parameter-free Bayesian approach, referred to as sparse learning via iterative minimization (SLIM), is presented. SLIM provides good channel estimation performance along with reduced computational complexity compared to iterative adaptive approach (IAA). Moreover, RELAX-BLAST, which is a linear minimum mean-squared error (MMSE)-based symbol detection scheme, is implemented efficiently by making use of the conjugate gradient (CG) method and diagonalization properties of circulant matrices. The proposed algorithm requires only simple fast Fourier transform (FFT) operations and facilitates parallel implementations. These MIMO UAC techniques are evaluated using both simulated and in-water experimental examples. The 2008 Surface Processes and Acoustic Communications Experiment (SPACE08) experimental results show that the proposed MIMO UAC schemes can enjoy almost error-free performance even under severe ocean environments.

  • 11.
    Remouit, Flore
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Galeazzi, Roberto
    Technical Unievrsity of Denmark (DTU).
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Laser-based relative positioning system for underwater remotely operated vehicleIn: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Refereed)
    Abstract [en]

    This paper addresses the development, testing and verification of a relative positioning system for underwater vehicles. The position and orientation of the vehicle relative to a plane based target is estimated through a laser-based optical system. The sensor package consists of two green line-lasers and a camera. The image processing algorithm is built on the probabilistic Hough transform and a light but robust filtering method. This decreases the computational time to 13.6 ms per image. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas in heading is 2°.

  • 12.
    Remouit, Flore
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ruiz-Minguela, Pablo
    TECNALIA, Derio Bizkaia 48160, Spain.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Review of Electrical Connectors for Underwater Applications2018In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 43, no 4, p. 1037-1047Article in journal (Refereed)
    Abstract [en]

    The history of underwater electrical connectors is relativelynew: In 1858, the first transatlantic communication cable was created. Sincethen, the need for subsea electrical connectors has been growing very fastin the offshore industry. Today numerous companies offer a large choiceof underwater connectors and assemblies, and it can be intricate to distinguish the different technologies employed for each of them. However theuse, deployment, maintenance, and lifetime of any subsea equipment, froma simple sonar to a wave energy converter, relies on its connectors. Hencethe design of an underwater electrical connector is to be carefully lookedat, and especially for tailor-made applications that have more specific requirements. To produce a good connector, it is necessary to account for thermal, electrical, and mechanical properties, as well as to determine thebest materials that should be used for the application. Finally, connector issues go hand in hand with the deployment and operation of any electrical equipment, and it is of interest to review the different techniques for cable connection, as well as the challenges related to cable layout. Those challenges can be of different nature, but they should all be taken into account for any subsea connection.

  • 13.
    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.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Estimation of Stress in the Inner Framework Structure of a Single Heaving Buoy Wave Energy Converter2012In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 37, no 2, p. 309-317Article in journal (Refereed)
    Abstract [en]

    This paper details a method for strain measurements in the inner framework structure of the single heaving buoy Wave Energy Converter (WEC). This type of the WEC consists of a linear direct drive generator placed on the sea floor and connected to the floating buoy through the connection line.

    The study focuses on estimation of stress in the inner framework structure of the WEC using strain measurements in material. Stress in ocean structures is as important as maximum stress.The offshore experiment was made at the Lysekil research site a few kilometers from the Swedish west coast.Stresses had the maximum value when the translator hit an end stop. Interesting observations were made: compressive stress occurred in the framework crossbar at a sea state of 1.32 m waves, but both compressive and tensile stress occurred at a sea state of 3.2 m waves.

    A computational procedure employs good results. Error estimation is calculated and represented. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.

  • 14.
    Svensson, Olle
    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.
    Peak Force Measurements on a Cylindrical Buoy with Limited Elastic Mooring2014In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 39, no 2, p. 398-403Article in journal (Refereed)
    Abstract [en]

    This paper investigates the line force of a moored floating buoy. The experiment was the first experiment made at the Swedish wave energy research area located close to Lysekil on the Swedish west coast. The Lysekil project is run by the Swedish Centre for Renewable Electric Energy Conversion at Uppsala University.                  The experimental set-up consists of a cylindrical buoy, with a diameter of 3 m and a height of 0.8 m. The buoy is moored with a line connected to a set of springs in parallel with a rope.

    The rope in parallel with the springs represents the limited stroke length of a linear generator type wave energy converter. The measurement system consists of a force transducer between the buoy and the rope, a three axis accelerometer inside the buoy and a data logger remotely operated through the GSM network.

         The peak forces related to the significant wave height showed a trend of 33 kN/m. Trends was also calculated in 10 kN bins. The data could be used in fatigue simulations of similar devices. The result was used when dimensioning the wave energy converter that was installed in March 2006.

  • 15.
    Tyrberg, Simon
    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.
    Kurupath, Venugopalan
    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.
    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.
    Wave Buoy and Translator Motions - On-Site Measurements and Simulations2011In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 36, no 3, p. 377-385Article in journal (Refereed)
    Abstract [en]

    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.

  • 16.
    Tyrberg, Simon
    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.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment2010In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 35, no 3, p. 558-564Article in journal (Refereed)
    Abstract [en]

    This paper investigates the sensitivity of a wave power system to variations in still water levels and significant wave heights. The system consists of a floating point absorber connected to a linear generator on the seabed. Changing still water levels are expected to affect the power absorption, since they will displace the equilibrium position for the generator translator. Similarly, changing significant wave heights will affect the rate at which the translator leaves the stator. Both these effects will in some cases result in a smaller active area of the stator. A theoretical expression to describe this effect is derived, and compared to measured experimental values for the wave energy converter at the Lysekil research site. During the time of measurements, the still water levels at the site were in the range of [-0.70 m, +0.46 m], and the significant wave heights in the range of [0 m, 2.7 m]. The experimental values exhibit characteristics similar to those of the theoretical expression, especially with changing significant wave heights.

  • 17.
    Yuen, Katarina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grabbe, Mårten
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bouquerel, Mathias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Österberg, David
    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.
    Matching a permanent magnet synchronous generator to a fixed pitch vertical axis turbine for marine current energy conversion2009In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 1, p. 24-31Article in journal (Refereed)
    Abstract [en]

    Extracting energy from a free-flow marine current using a vertical axis fixed pitch turbine requires a generator that can handle varying speeds and loads, since such a turbine gives maximum power capture for a fixed tip speed ratio. A prototype of such a generator has been designed and constructed. In this paper, its variable speed and load operation is evaluated, both in terms of how the constructed generator performs in relation to simulations, and in terms of how the generator could perform with three different fixed pitch turbines. Measurements of root mean square (RMS) voltage and current differ 10% from simulations. Performance analysis with example turbines shows that the generator can match fixed tip speed ratio operation of several turbines for current speeds between 0.5 and 2.5 m/s.

1 - 17 of 17
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