Electrical System of a Wave Power Plant

Abstract: Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several techniques to convert the energy in the ocean waves into electric energy. The wave energy converter presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. By keeping the generator as simple as possible and minimizing the number of mechanical parts, the lifetime of the generator is believed to increase. To convert and interconnect the power from the generators, marine substations are used. The marine substation will be placed on the seabed and it will convert the AC with variable amplitude and variable frequency from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the conversion, the rectification and filtering. The purpose with the study was to investigate how the generator will operate when it is connected to a non-linear load and to obtain guidelines on how larger systems could be designed. Another aim with the experiment was to see to which extent the voltage and power out from the generator can be smoothened. Offshore experiments and simulations have been done on a full scale generator connected to a diode rectifier and filter. The results show that a smooth DC output voltage after the rectifier has small ripple content. The kind of load and value of load will have an impact on the generators ability to absorb and produce power. The highest amount of absorbed power is achieved at the highest damping of the system. However, the highest damping function does not necessarily coincide with the maximum produced power. In connection to the installation of two new wave energy converters on the Swedish west coast, a marine substation will be launched at the site. Laboratory tests have been done on the marine substation and it worked as expected and the experimental data had a good agreement with the simulated data.

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