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This is an author-produced version of a paper published in IEEE Journal of Oceanic Engineering. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the published paper: Yuen K., Thomas K., Grabbe M., Deglaire P., Bouquerel M., Österberg D., Leijon M. "Matching a permanent magnet synchronous generator to a fixed pitch vertical axis turbine for marine current energy conversion" IEEE Journal of Oceanic Engineering, 2009, 34(1) Access to the published version may require subscription. I. INTRODUCTIONF REE flow marine currents, i.e. unregulated water courses, tides and other ocean currents, are an energy resource yet to be utilized on a commercial scale. Without dams, this nonfossil source can give an environmentally benign contribution to the world electricity production. The European tidal potential alone has been estimated to be 39-58 TWh annually [1]- [3]. A number of projects involved with extracting energy from this resource exist, and most concepts are similar to wind energy converters in that they include a turbine and a generator, e.g. [4]- [7].Wind power is similar to marine current energy as it is concerned with harnessing the kinetic energy in a flowing fluid, and there are many relevant comparisons concerning underlying physics, practical engineering experience, etc. However, there are also a number of significant differences, e.g. resource characteristics. As most parts of the system will be submerged in water and thus not easily accessible, it is good to try to minimize needs for maintenance and repair by avoiding mechanically complex systems with many moving parts. In [8], it is concluded that up to 20 percent of the downtime for a wind power plant is due to gearbox failures, and that the majority of these failures are due to wear. Therefore, avoiding gearboxes, yawing and blade pitching is likely to be beneficial Manuscript

Abstract:A low-speed permanent magnet (PM) cable wound generator for electrical energy conversion from marine or tidal currents has been designed and constructed. A key feature of this variable speed direct drive generator is its capability to efficiently generate electricity from tidal currents with very low velocities, in the order of 1 m/s. In arriving at an appropriate design for the generator typical characteristics of tidal currents were considered. Using these characteristics as input, and accounting for the electromagnetic losses, detailed computer simulations using a finite-element method software were carried out to come up with the final design. Various parameters that can influence the generator design are presented.An experimental set-up has been constructed based on the above-mentioned design in order to study the electrical and mechanical performance of the generator through a variety of experiments. The power input for this set-up is a variable speed motor, capable of operating the generator at rotational speeds of 0-16 r/min, representing tidal currents with very low velocities. The generator presented in this paper may be beneficial for a better understanding of an appropriate design and layout of tidal energy conversion systems.

Some countries are facing issues on freshwater and electricity production, which can be addressed with the use of renewable energy powered desalination systems. In the following study, a reverse osmosis desalination plant powered by marine current energy converters is suggested. The marine current energy converters are designed at Uppsala University in Sweden, specifically for utilizing low water speeds (1-2 m/s). Estimations on freshwater production for such a system, in South Africa, facing the Indian Ocean was presented and discussed. It is concluded that the desalination plant cannot by itself supply freshwater for a population all the time, due to periods of too low water speeds (<1 m/s), but for 75% of the time. By using ten marine current energy converters, each with a nominal power rating of 7.5 kW, combined with a reverse osmosis desalination plant and water storage capacity of 2800 m 3 , it is possible to cover the basic freshwater demand of 5000 people. More studies on the hydrokinetic resource of the Western Indian Ocean, system cost, technology development, environmental and social aspects are necessary for more accurate results.

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