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The damping effect, induced inside the linear generator, is a vital factor to improve the conversion efficiency of wave energy converters (WEC). As part of the mechanical design, the translator mass affects the damping force and eventually affects the performance of the WEC by converting wave energy into electricity. This paper proposes research on the damping effect coupled with translator mass regarding the generated power from WEC. Complicated influences from ocean wave climates along the west coast of Sweden are also included. This paper first compares three cases of translator mass with varied damping effects. A further investigation on coupling effects is performed using annual energy absorption under a series of sea states. Results suggest that a heavier translator may promote the damping effect and therefore improve the power production. However, the hinder effect is also observed and analyzed in specific cases. In this paper, the variations in the optimal damping coefficient are observed and discussed along with different cases.
Yue Hong; Mikael Eriksson; Cecilia Boström; Jianfei Pan; Yun Liu; Rafael Waters. Damping Effect Coupled with the Internal Translator Mass of Linear Generator-Based Wave Energy Converters. Energies 2020, 13, 4424 .
AMA StyleYue Hong, Mikael Eriksson, Cecilia Boström, Jianfei Pan, Yun Liu, Rafael Waters. Damping Effect Coupled with the Internal Translator Mass of Linear Generator-Based Wave Energy Converters. Energies. 2020; 13 (17):4424.
Chicago/Turabian StyleYue Hong; Mikael Eriksson; Cecilia Boström; Jianfei Pan; Yun Liu; Rafael Waters. 2020. "Damping Effect Coupled with the Internal Translator Mass of Linear Generator-Based Wave Energy Converters." Energies 13, no. 17: 4424.
The working principle of the wave energy converter (WEC) developed at Uppsala University (UU) is based on a heaving point absorber with a linear generator. The generator is placed on the seafloor and is connected via a steel wire to a buoy floating on the surface of the sea. The generator produces optimal power when the translator's oscillations are centered with respect to the stator. However, due to the tides or other changes in sea level, the translator's oscillations may shift towards the upper or lower limit of the generator's stroke length, resulting in a limited stroke and a consequent reduction in power production. A compensator has been designed and developed in order to keep the generator's translator centered, thus compensating for sea level variations. This paper presents experimental tests of the compensator in a lab environment. The wire adjustments are based on online sea level data obtained from the Swedish Meteorological and Hydrological Institute (SMHI). The objective of the study was to evaluate and optimize the control and communication system of the device. As the device will be self-powered with solar and wave energy, the paper also includes estimations of the power consumption and a control strategy to minimize the energy requirements of the whole system. The application of the device in a location with high tides, such as Wave Hub, was analyzed based on offline tidal data. The results show that the compensator can minimize the negative effects of sea level variations on the power production at the WEC. Although the wave energy concept of UU is used in this study, the developed system is also applicable to other WECs for which the line length between seabed and surface needs to be adjusted.
Mohd Nasir Ayob; Valeria Castellucci; Johan Abrahamsson; Rafael Waters. A Remotely Controlled Sea Level Compensation System for Wave Energy Converters. Energies 2019, 12, 1946 .
AMA StyleMohd Nasir Ayob, Valeria Castellucci, Johan Abrahamsson, Rafael Waters. A Remotely Controlled Sea Level Compensation System for Wave Energy Converters. Energies. 2019; 12 (10):1946.
Chicago/Turabian StyleMohd Nasir Ayob; Valeria Castellucci; Johan Abrahamsson; Rafael Waters. 2019. "A Remotely Controlled Sea Level Compensation System for Wave Energy Converters." Energies 12, no. 10: 1946.
This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, small-scale electricity generation in the buoy is needed to power a tidal compensating system designed to increase the performance of the WEC in areas with high tides. The two considered and modeled concepts are an oscillating water column (OWC) and a heaving point absorber. The results indicate that the OWC is too small for the task and does not produce enough energy. On the other hand, the results show that a hybrid system composed of a small heaving point absorber combined with a solar energy system would be able to provide a requested minimum power of around 37.7 W on average year around. The WEC and solar panel complement each other, as the WEC produces enough energy by itself during wintertime (but not in the summer), while the solar panel produces enough energy in the summer (but not in the winter).
Mohd Nasir Ayob; Valeria Castellucci; Malin Göteman; Joakim Widen; Johan Abrahamsson; Jens Engstrom; Rafael Waters. Small-Scale Renewable Energy Converters for Battery Charging. Journal of Marine Science and Engineering 2018, 6, 26 .
AMA StyleMohd Nasir Ayob, Valeria Castellucci, Malin Göteman, Joakim Widen, Johan Abrahamsson, Jens Engstrom, Rafael Waters. Small-Scale Renewable Energy Converters for Battery Charging. Journal of Marine Science and Engineering. 2018; 6 (1):26.
Chicago/Turabian StyleMohd Nasir Ayob; Valeria Castellucci; Malin Göteman; Joakim Widen; Johan Abrahamsson; Jens Engstrom; Rafael Waters. 2018. "Small-Scale Renewable Energy Converters for Battery Charging." Journal of Marine Science and Engineering 6, no. 1: 26.
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
Linnea Sjökvist; Malin Göteman; Magnus Rahm; Rafael Waters; Olle Svensson; Erland Strömstedt; Mats Leijon. Calculating buoy response for a wave energy converter—A comparison of two computational methods and experimental results. Theoretical and Applied Mechanics Letters 2017, 7, 164 -168.
AMA StyleLinnea Sjökvist, Malin Göteman, Magnus Rahm, Rafael Waters, Olle Svensson, Erland Strömstedt, Mats Leijon. Calculating buoy response for a wave energy converter—A comparison of two computational methods and experimental results. Theoretical and Applied Mechanics Letters. 2017; 7 (3):164-168.
Chicago/Turabian StyleLinnea Sjökvist; Malin Göteman; Magnus Rahm; Rafael Waters; Olle Svensson; Erland Strömstedt; Mats Leijon. 2017. "Calculating buoy response for a wave energy converter—A comparison of two computational methods and experimental results." Theoretical and Applied Mechanics Letters 7, no. 3: 164-168.
The energy absorption of the wave energy converters (WEC) characterized by a limited stroke length —like the point absorbers developed at Uppsala University—depends on the sea level variation at the deployment site. In coastal areas characterized by high tidal ranges, the daily energy production of the generators is not optimal. The study presented in this paper quantifies the effects of the changing sea level at the Wave Hub test site, located at the south-west coast of England. This area is strongly affected by tides: the tidal height calculated as the difference between the Mean High Water Spring and the Mean Low Water Spring in 2014 was about 6.6 m. The results are obtained from a hydro-mechanic model that analyzes the behaviour of the point absorber at the Wave Hub, taking into account the sea state occurrence scatter diagram and the tidal time series at the site. It turns out that the impact of the tide decreases the energy absorption by 53%. For this reason, the need for a tidal compensation system to be included in the design of the WEC becomes compelling. The economic advantages are evaluated for different scenarios: the economic analysis proposed within the paper allows an educated guess to be made on the profits. The alternative of extending the stroke length of the WEC is investigated, and the gain in energy absorption is estimated.
Valeria Castellucci; Mikael Eriksson; Rafael Waters. Impact of Tidal Level Variations on Wave Energy Absorption at Wave Hub. Energies 2016, 9, 843 .
AMA StyleValeria Castellucci, Mikael Eriksson, Rafael Waters. Impact of Tidal Level Variations on Wave Energy Absorption at Wave Hub. Energies. 2016; 9 (10):843.
Chicago/Turabian StyleValeria Castellucci; Mikael Eriksson; Rafael Waters. 2016. "Impact of Tidal Level Variations on Wave Energy Absorption at Wave Hub." Energies 9, no. 10: 843.
The Lysekil wave energy converter (WEC), developed by the wave energy research group of Uppsala University, has evolved through a variety of mechanical designs since the first prototype was installed in 2006. The hundreds of engineering decisions made throughout the design processes have been based on a combination of theory, know-how from previous experiments, and educated guesses. One key parameter in the design of the WECs linear generator is the stroke length. A long stroke requires a taller WEC with associated economical and mechanical challenges, but a short stroke limits the power production. The 2-m stroke of the current WECs has been an educated guess for the Swedish wave climate, though the consequences of this choice on energy absorption have not been studied. When the WEC technology is considered for international waters, with larger waves and challenges of energy absorption and survivability, the subject of stroke length becomes even more relevant. This paper studies the impact of generator stroke length on energy absorption for three sites off the coasts of Sweden, Chile and Scotland. 2-m, 4-m, and unlimited stroke are considered. Power matrices for the studied WEC prototype are presented for each of the studied stroke lengths. Presented results quantify the losses incurred by a limited stroke. The results indicate that a 2-m stroke length is likely to be a good choice for Sweden, but 4-m is likely to be necessary in more energetic international waters.
Yue Hong; Mikael Eriksson; Cecilia Boström; Rafael Waters. Impact of Generator Stroke Length on Energy Production for a Direct Drive Wave Energy Converter. Energies 2016, 9, 730 .
AMA StyleYue Hong, Mikael Eriksson, Cecilia Boström, Rafael Waters. Impact of Generator Stroke Length on Energy Production for a Direct Drive Wave Energy Converter. Energies. 2016; 9 (9):730.
Chicago/Turabian StyleYue Hong; Mikael Eriksson; Cecilia Boström; Rafael Waters. 2016. "Impact of Generator Stroke Length on Energy Production for a Direct Drive Wave Energy Converter." Energies 9, no. 9: 730.
The bivariate joint distribution of the significant wave height and the wave period is of great importance in characterizing the wave climate at a wave energy converter test site. In this paper, we investigate bivariate joint distribution modeling of the wave climate at the Lysekil wave energy converter test site off the Swedish west coast. This study is based on 9 years of wave observations at the test site from 2005 to 2013. Archimedean Copulas are used for the bivariate joint distribution modeling of the significant wave height and the wave period. Measured wave data is compared with simulated wave climate data for the Lysekil test site using three Archimedean Copula models, the Clayton, Frank and Gumbel copulas. The R-squared statistical test yields a better goodness of fit for the Gumbel copula compared to the other two copulas. In addition, the Archimedean Copula method is applied to the measured wave climate data from two other sites to illustrate the general applicability. It shows that the Archimedean Copulas exhibits stable performance with good accuracy in characterizing the wave climate and they can be employed for forecasting the wave energy resource and assessing the survivability of wave energy converters.
Wei Li; Jan Isberg; Rafael Waters; Olle Svensson; Mats Leijon; Wenchuang Chen; Jens Engström. Bivariate joint distribution modeling of wave climate data using a copula method. International Journal of Energy and Statistics 2016, 4, 1 .
AMA StyleWei Li, Jan Isberg, Rafael Waters, Olle Svensson, Mats Leijon, Wenchuang Chen, Jens Engström. Bivariate joint distribution modeling of wave climate data using a copula method. International Journal of Energy and Statistics. 2016; 4 (3):1.
Chicago/Turabian StyleWei Li; Jan Isberg; Rafael Waters; Olle Svensson; Mats Leijon; Wenchuang Chen; Jens Engström. 2016. "Bivariate joint distribution modeling of wave climate data using a copula method." International Journal of Energy and Statistics 4, no. 3: 1.
The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005–2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site. The mixed-distribution model is also applied to measured wave data from four other sites and it provides an illustration of the general applicability of the proposed model. The methodologies used in this paper can be applied to general wave climate analysis of wave energy test sites to estimate extreme waves for the survivability assessment of wave energy converters and characterize the long wave climate to forecast the wave energy resource of the test sites and the energy production of the wave energy converters.
Wei Li; Jan Isberg; Rafael Waters; Jens Engström; Olle Svensson; Mats Leijon. Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction. Energies 2016, 9, 396 .
AMA StyleWei Li, Jan Isberg, Rafael Waters, Jens Engström, Olle Svensson, Mats Leijon. Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction. Energies. 2016; 9 (6):396.
Chicago/Turabian StyleWei Li; Jan Isberg; Rafael Waters; Jens Engström; Olle Svensson; Mats Leijon. 2016. "Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction." Energies 9, no. 6: 396.
Power generation from wave power has a large potential to contribute to our electric energy production, and today, many wave power projects are close to be commercialized. However, one key issue to solve for many projects is to decrease the cost per installed kW. One way to do this is to investigate which parameters that have a significant impact on the wave energy converters (WEC) performance. In this paper, experimental results on power absorption from a directly driven point absorbing WEC are presented. The experiments have been carried out at the Lysekil research site in Sweden. To investigate the performance of the WEC, the absorbed power and the speed of the translator are compared. The result confirms that the buoy size and the translator weight have a large impact on the power absorption from the generator. By optimizing the buoy size and translator weight, the WEC is believed to produce power more evenly over the upward and downward cycle. Moreover, to predict the maximum power limit during normal operation, a simulation model has been derived. The results correlates well with experimental data during normal operation.
Erik Lejerskog; Cecilia Boström; Ling Hai; Rafael Waters; Mats Leijon. Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site. Renewable Energy 2015, 77, 9 -14.
AMA StyleErik Lejerskog, Cecilia Boström, Ling Hai, Rafael Waters, Mats Leijon. Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site. Renewable Energy. 2015; 77 ():9-14.
Chicago/Turabian StyleErik Lejerskog; Cecilia Boström; Ling Hai; Rafael Waters; Mats Leijon. 2015. "Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site." Renewable Energy 77, no. : 9-14.
The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed.
Valeria Castellucci; Johan Abrahamsson; Tobias Kamf; Rafael Waters. Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters. Energies 2015, 8, 3272 -3291.
AMA StyleValeria Castellucci, Johan Abrahamsson, Tobias Kamf, Rafael Waters. Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters. Energies. 2015; 8 (4):3272-3291.
Chicago/Turabian StyleValeria Castellucci; Johan Abrahamsson; Tobias Kamf; Rafael Waters. 2015. "Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters." Energies 8, no. 4: 3272-3291.
Valeria Castellucci; Johan Abrahamsson; Olle Svensson; Rafael Waters. Algorithm for the calculation of the translator position in permanent magnet linear generators. Journal of Renewable and Sustainable Energy 2014, 6, 063102 .
AMA StyleValeria Castellucci, Johan Abrahamsson, Olle Svensson, Rafael Waters. Algorithm for the calculation of the translator position in permanent magnet linear generators. Journal of Renewable and Sustainable Energy. 2014; 6 (6):063102.
Chicago/Turabian StyleValeria Castellucci; Johan Abrahamsson; Olle Svensson; Rafael Waters. 2014. "Algorithm for the calculation of the translator position in permanent magnet linear generators." Journal of Renewable and Sustainable Energy 6, no. 6: 063102.
A wave energy converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common dc-bus. The dc voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower dc-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal dc-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the dc-level seen by the generator influence the power output. The results indicate that higher dc-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which dc-level is chosen.
Rickard Ekström; Venugopalan Kurupath; Cecilia Boström; Rafael Waters; Mats Leijon. Evaluating Constant DC-Link Operation of Wave Energy Converter. Journal of Dynamic Systems, Measurement, and Control 2013, 136, 014501 .
AMA StyleRickard Ekström, Venugopalan Kurupath, Cecilia Boström, Rafael Waters, Mats Leijon. Evaluating Constant DC-Link Operation of Wave Energy Converter. Journal of Dynamic Systems, Measurement, and Control. 2013; 136 (1):014501.
Chicago/Turabian StyleRickard Ekström; Venugopalan Kurupath; Cecilia Boström; Rafael Waters; Mats Leijon. 2013. "Evaluating Constant DC-Link Operation of Wave Energy Converter." Journal of Dynamic Systems, Measurement, and Control 136, no. 1: 014501.
Recent studies show that there is a correlation between water level and energy absorption values for the studied wave energy converters: the absorption decreases when the water levels deviate from average. The situation appears during tides when the water level changes significantly. The main objective of the paper is to present a first attempt to increase the energy absorption during tides by designing and realizing a small-scale model of a point absorber equipped with a device that is able to adjust the length of the rope connected to the generator. The adjustment is achieved by a screw that moves upwards in the presence of low tides and downwards in the presence of high tides. Numerical results as well as experimental tests suggest that the solution adopted to minimize the tidal effect on the power generation shows potential for further development.
Valeria Castellucci; Rafael Waters; Markus Eriksson; Mats Leijon. Tidal effect compensation system for point absorbing wave energy converters. Renewable Energy 2013, 51, 247 -254.
AMA StyleValeria Castellucci, Rafael Waters, Markus Eriksson, Mats Leijon. Tidal effect compensation system for point absorbing wave energy converters. Renewable Energy. 2013; 51 ():247-254.
Chicago/Turabian StyleValeria Castellucci; Rafael Waters; Markus Eriksson; Mats Leijon. 2013. "Tidal effect compensation system for point absorbing wave energy converters." Renewable Energy 51, no. : 247-254.
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.
Cecilia Bostrom; Boel Ekergard; Rafael Waters; Mikael Eriksson; Mats Leijon. Linear Generator Connected to a Resonance-Rectifier Circuit. IEEE Journal of Oceanic Engineering 2013, 38, 255 -262.
AMA StyleCecilia Bostrom, Boel Ekergard, Rafael Waters, Mikael Eriksson, Mats Leijon. Linear Generator Connected to a Resonance-Rectifier Circuit. IEEE Journal of Oceanic Engineering. 2013; 38 (2):255-262.
Chicago/Turabian StyleCecilia Bostrom; Boel Ekergard; Rafael Waters; Mikael Eriksson; Mats Leijon. 2013. "Linear Generator Connected to a Resonance-Rectifier Circuit." IEEE Journal of Oceanic Engineering 38, no. 2: 255-262.
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.
Cecilia Boström; Magnus Rahm; Olle Svensson; Erland Strömstedt; Andrej Savin; Rafael Waters; Mats Leijon. Temperature Measurements in a Linear Generator and Marine Substation for Wave Power. Journal of Offshore Mechanics and Arctic Engineering 2011, 134, 021901 .
AMA StyleCecilia Boström, Magnus Rahm, Olle Svensson, Erland Strömstedt, Andrej Savin, Rafael Waters, Mats Leijon. Temperature Measurements in a Linear Generator and Marine Substation for Wave Power. Journal of Offshore Mechanics and Arctic Engineering. 2011; 134 (2):021901.
Chicago/Turabian StyleCecilia Boström; Magnus Rahm; Olle Svensson; Erland Strömstedt; Andrej Savin; Rafael Waters; Mats Leijon. 2011. "Temperature Measurements in a Linear Generator and Marine Substation for Wave Power." Journal of Offshore Mechanics and Arctic Engineering 134, no. 2: 021901.
This paper presents calculations of the varying inductances profile for a synchronous linear surface mounted permanent magnet generator in an ABC reference system. Calculations are performed by utilizing the reluctance term, known from analytic calculations and finite element method simulations. With the inductance term identified, the voltage difference between the generator’s no load and load voltage can be calculated and an external circuit can be designed for optimal use of the generator. Two different operation intervals of the linear generator are considered and the results are discussed. The result indicates that time costly finite element simulations can be replaced with simple analytical calculations for a surface mounted permanent magnet linear generator.
Boel Ekergård; Rafael Waters; Mats Leijon. Prediction of the Inductance in a Synchronous Linear Permanent Magnet Generator. Journal of Electromagnetic Analysis and Applications 2011, 03, 155 -159.
AMA StyleBoel Ekergård, Rafael Waters, Mats Leijon. Prediction of the Inductance in a Synchronous Linear Permanent Magnet Generator. Journal of Electromagnetic Analysis and Applications. 2011; 03 (05):155-159.
Chicago/Turabian StyleBoel Ekergård; Rafael Waters; Mats Leijon. 2011. "Prediction of the Inductance in a Synchronous Linear Permanent Magnet Generator." Journal of Electromagnetic Analysis and Applications 03, no. 05: 155-159.
An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.
Cecilia Boström; Erik Lejerskog; Simon Tyrberg; Olle Svensson; Rafael Waters; Andrej Savin; Björn Bolund; Mikael Eriksson; Mats Leijon. Experimental Results From an Offshore Wave Energy Converter. Journal of Offshore Mechanics and Arctic Engineering 2010, 132, 041103 .
AMA StyleCecilia Boström, Erik Lejerskog, Simon Tyrberg, Olle Svensson, Rafael Waters, Andrej Savin, Björn Bolund, Mikael Eriksson, Mats Leijon. Experimental Results From an Offshore Wave Energy Converter. Journal of Offshore Mechanics and Arctic Engineering. 2010; 132 (4):041103.
Chicago/Turabian StyleCecilia Boström; Erik Lejerskog; Simon Tyrberg; Olle Svensson; Rafael Waters; Andrej Savin; Björn Bolund; Mikael Eriksson; Mats Leijon. 2010. "Experimental Results From an Offshore Wave Energy Converter." Journal of Offshore Mechanics and Arctic Engineering 132, no. 4: 041103.
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 L1 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.
Simon Tyrberg; Rafael Waters; Mats Leijon. Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment. IEEE Journal of Oceanic Engineering 2010, 35, 558 -564.
AMA StyleSimon Tyrberg, Rafael Waters, Mats Leijon. Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment. IEEE Journal of Oceanic Engineering. 2010; 35 (3):558-564.
Chicago/Turabian StyleSimon Tyrberg; Rafael Waters; Mats Leijon. 2010. "Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment." IEEE Journal of Oceanic Engineering 35, no. 3: 558-564.
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.
Cecilia Boström; Magnus Rahm; Olle Svensson; Erland Strömstedt; Andrej Savin; Rafael Waters; Mats Leijon. Temperature Measurements in a Linear Generator and Marine Substation for Wave Power. 29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 3 2010, 545 -552.
AMA StyleCecilia Boström, Magnus Rahm, Olle Svensson, Erland Strömstedt, Andrej Savin, Rafael Waters, Mats Leijon. Temperature Measurements in a Linear Generator and Marine Substation for Wave Power. 29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 3. 2010; ():545-552.
Chicago/Turabian StyleCecilia Boström; Magnus Rahm; Olle Svensson; Erland Strömstedt; Andrej Savin; Rafael Waters; Mats Leijon. 2010. "Temperature Measurements in a Linear Generator and Marine Substation for Wave Power." 29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 3 , no. : 545-552.
An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the ocean floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measure station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the existing wave energy system of the Islandsberg project. Special attention will be given to the power absorption by the generator when it is connected to a non linear load.
Cecilia Bostro¨m; Erik Lejerskog; Simon Tyrberg; Olle Svensson; Rafael Waters; Andrej Savin; Bjo¨rn Bolund; Mikael Eriksson; Mats Leijon. Experimental Results From an Offshore Wave Energy Converter. Volume 3: Pipeline and Riser Technology; Ocean Space Utilization 2008, 653 -657.
AMA StyleCecilia Bostro¨m, Erik Lejerskog, Simon Tyrberg, Olle Svensson, Rafael Waters, Andrej Savin, Bjo¨rn Bolund, Mikael Eriksson, Mats Leijon. Experimental Results From an Offshore Wave Energy Converter. Volume 3: Pipeline and Riser Technology; Ocean Space Utilization. 2008; ():653-657.
Chicago/Turabian StyleCecilia Bostro¨m; Erik Lejerskog; Simon Tyrberg; Olle Svensson; Rafael Waters; Andrej Savin; Bjo¨rn Bolund; Mikael Eriksson; Mats Leijon. 2008. "Experimental Results From an Offshore Wave Energy Converter." Volume 3: Pipeline and Riser Technology; Ocean Space Utilization , no. : 653-657.