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Ocean Wave Energy: Underwater Substation System for Wave Energy

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Ocean Wave Energy: Underwater Substation System for Wave Energy ! " #$#%#""#&' ISBN 5675777 8 7 9 7 : 7 8 8 8 ; 5 8 7 ; < =:< 7 ; 8 7 8 ! " !" !# $%&'! !"()%*+* ! > ;?979 ;@?5675777 75A CC 8C D E 75F Till min älskade son, Emil. List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I Stålberg, M., Waters, R., Eriksson, M., Danielsson, O., Thorburn, K., Bernhoff, H., and Leijon, M. “Full-Scale Testing of PM Linear Gener- ator for Point Absorber WEC”. Proceedings of the 6th European Wave and Tidal Energy Conference, EWTEC, Glasgow, UK, September, 2005. II Waters, R., Stålberg, M., Danielsson, O., Svensson, O., Gustafsson, S., Strömstedt, E., Eriksson, M., Sundberg, J., and Leijon, M. “Experimen- tal results from sea trials of an offshore wave energy system”. Applied Physics Letters, 90:034105, 2007. III Stålberg, M., Waters, R., Danielsson, O., and Leijon, M. “Influence of Generator Damping on Peak Power and Variance of Power for a Di- rect Drive Wave Energy Converter”. Journal of Offshore Mechanics and Arctic Engineering, 130(3), 2008. IV Waters, R., Rahm, M., Svensson, O., Strömstedt, E., Boström, C., Sundberg, J., and Leijon, M. “Energy absorption in response to wave frequency and amplitude - offshore experiments on a wave energy converter”. Submitted to AIP Journal of Renewable and Sustainable Energy, January 20, 2010. V Engström, J., Waters, R., Stålberg, M., Strömstedt, E., Eriksson, M., Isberg, J., Henfridsson, U., Bergman, K., Asmussen, J., and Leijon, M. “Offshore experiments on a direct-driven Wave Energy Converter”. Proceedings of the 7th European Wave and Tidal Energy Conference, EWTEC, Porto, Portugal, September, 2007. VI Boström, C., Lejerskog, E., Stålberg, M., Thorburn, K., and Leijon, M. “Experimental results of rectification and filtration from an offshore wave energy system”. Renewable Energy, 34(5):1381-1387, 2009. VII Boström, C., Waters, R., Lejerskog, E., Svensson, O., Stålberg, M., Strömstedt, E., and Leijon, M. “Study of a Wave Energy Converter Con- nected to a Nonlinear Load”. IEEE Journal of Oceanic Engineering, 34(2), 2009. VIII Leijon, M., Boström, C., Danielsson, O., Gustafsson, S., Haikonen, K., Langhamer, O., Strömstedt, E., Stålberg, M., Sundberg, J., Svensson, O., Tyrberg, S., and Waters, R. “Wave Energy from the North Sea: Experiences from the Lysekil Research Site”. Surveys in Geophysics, 29(3), 2008. IX Leijon, M., Waters, R., Rahm, M., Svensson, O., Boström, C., Strömst- edt, E., Engström, J., Tyrberg, S., Savin, A., Gravråkmo, H., Bernhoff, H., Sundberg, J., Isberg, J., Ågren, O., Danielsson, O., Eriksson, M., Lejerskog, E., Bolund, B., Gustafsson, S., and Thorburn, K.“Catch the wave to electricity”. IEEE Power and Energy Magazine, 7(1):50-54, 2009. X Boström, C., Rahm, M., Svensson, O., Strömstedt, E., Savin, A., Wa- ters, R., and Leijon, M. “Temperature measurements in a linear gen- erator and marine substation for wave power”. Submitted to the 29th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2010, Shanghai, China, June 6-11, 2010. XI Rahm, M., Boström, C., Svensson, O., Grabbe, M., Bülow, F., and Lei- jon, M. “Laboratory experimental verification of a marine substation”. Proceedings of the 8th European Wave and Tidal Energy Conference, EWTEC, Uppsala, Sweden, September, 2009. XII Svensson, O., Boström, C., Rahm, M., and Leijon, M. “Description of the control and measurement system used in the Low Voltage Marine Substation at the Lysekil research site”. Proceedings of the 8th Euro- pean Wave and Tidal Energy Conference, EWTEC, Uppsala, Sweden, September, 2009. XIII Rahm, M., Boström, C., Svensson, O., Grabbe, M., Bülow, F. and Lei- jon, M. “Offshore underwater substation for wave energy converter ar- rays”. Submitted to IET Renewable Power Generation, November 20, 2009. XIV Rahm, M., Svensson, O., Boström, C., Waters, R. and Leijon, M. “Power smoothing in an offshore wave energy converter array”. Submitted to AIP Journal of Renewable and Sustainable Energy, November 3, 2009. XV Boström, C., Svensson, O., Rahm, M., Lejerskog, E., Savin, A., Ström- stedt, E., Engström, J., Gravråkmo, H., Haikonen, K., Waters, R., Björk- löf, D., Johansson, T., Sundberg, J., and Leijon, M. “Design proposal of electrical system for linear generator wave power plants”. Proceedings of the 35th Annual Conference of the IEEE Industrial Electronics Soci- ety, IECON, Porto, Portugal, November, 2009. Reprints were made with permission from the publishers. The author has contributed to the following papers which are not included in the thesis. XVI Stålberg, M., Waters, R., Danielsson, O., Leijon, M. “Influence of Gen- erator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter”. Proceedings of the 26th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2007, San Diego, California, USA, 2007. XVII Tyrberg, S., Stålberg, M., Boström, C., Waters, R., Svensson, O., Strömstedt, E., Savin, A., Engström, J., Langhamer, O., Gravråkmo, H., Haikonen, K., Tedelid, J., Sundberg, J., and Leijon, M. “The Lysekil Wave Power Project: Status Update”. Proceedings of the 10th World Renewable Energy Conference, WREC, Glasgow, UK, 2008. XVIII Solum, A., Deglaire, P., Eriksson, S., Stålberg, M., Leijon, M., and Bernhoff, H. “Design of a 12kW vertical axis wind turbine equipped with a direct driven PM synchronous generator”. Proceedings of the Eu- ropean Wind Energy Conference & Exhibition, EWEC, Athens, Greece, 2006. Contents 1 Introduction . ........................................ 15 1.1 Renewable energy resource base . .................... 15 1.2 Wave energy conversion principles . .................... 15 1.2.1 Oscillating water column devices ................... 16 1.2.2 Overtopping devices ............................ 17 1.2.3 Oscillating body devices . ........................ 18 1.3 The Uppsala University wave energy concept . ........... 20 1.4 The Lysekil wave energy research site . ................ 23 2 Background . ........................................ 27 2.1 Historic overview of point absorbers .................... 27 2.2 Hydrodynamical properties of the Uppsala PA . ........... 30 2.3 Power smoothing by energy storage . .................... 30 2.4 Power smoothing by spatial distribution . ................ 31 2.5 Linear generators . .................................. 32 2.6 Grid connection schemes for offshore renewables . ....... 34 2.7 European wave energy test sites and pilot zones . ........... 36 2.8 Grid connection . .................................. 39 2.8.1 Regulations . ................................. 39 2.8.2 Power quality in WEC electrical systems . .......... 40 3 Theory . ............................................ 41 3.1 Real ocean waves .................................. 41 3.1.1 The dispersion relation . ........................ 41 3.1.2 Wavelength, speed and period . ................... 42 3.1.3 Wave spectrum ................................ 42 3.2 Point absorbers . .................................. 43 3.2.1 Single point absorbers . ........................ 43 3.2.2 Point absorber arrays ............................ 45 3.3 Magnetism . ...................................... 45 3.3.1 The origin of magnetic flux density . ............... 45 3.3.2 Hard magnetic materials . ........................ 47 3.3.3 Soft magnetic materials . ........................ 48 3.4 Electromagnetic losses in electrical machines . ........... 48 3.4.1 Hysteresis losses . ............................ 49 3.4.2 Eddy-current losses . ............................ 49 3.4.3 Anomalous losses . ............................ 50 3.4.4 Resistive losses ................................ 50 3.5 No-load voltage of an LG in sinusoidal oscillation . ....... 51 3.6 Damping . ...................................... 51 3.7 Three-phase diode rectifiers . ......................... 52 3.8 Three-phase inverters . ............................. 52 3.8.1 The insulated gate bipolar transistor . ............... 53 3.8.2 Pulse width modulation . ........................ 54 3.8.3 Losses in switched semiconductor devices . .......... 54 4 Experimental work . ................................... 57 4.1 Linear generator . .................................. 58 4.2 Sea cable at the Lysekil research site .................... 59 4.3 On-shore measuring station . ......................... 59 4.4 Wave energy converter . ............................. 59 4.4.1 Buoy line guidance system ........................ 60 4.4.2 Electrical connection ............................ 63 4.5 Offshore underwater collector substation . ................ 63 4.5.1 Mechanical design . ............................ 64 4.5.2 Main circuit . ................................. 65 4.5.3 Auxiliary systems . ............................ 69 4.5.4 Cables and connectors . ........................ 70 4.5.5 Maintenance . ................................. 70 4.6 Measurement inaccuracy ............................. 72 4.6.1 Voltage and current measurements . ............... 72 4.6.2 Temperature sensors ............................ 72 5 Summary of results and discussion ......................... 73 5.1
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