Wave Energy Conversion: Direct Coupled Point Absorber in Heave with Induction Machine as Power Take Off

Abstract

In the area of offshore renewable, wave energy can give great contribution. There has been research for developing wave energy converters since the late eighteenth century when the first patent was applied for in 1799 [1], without any remarkable breakthrough. This master thesis will discuss the topic of wave energy conversion by a point absorber in heave with a directly coupled induction machine power take off. A wave to wire approach has been attempted in this thesis. The tool needed is a hydrodynamic model combined with a full model of an electrical generator. The tool is developed to investigate challenges for wave energy conversion by direct coupled induction machine as power take off. Simulations have been carried out in the time domain to study the motion of a point absorber in heave for energy extraction. Previous research in wind power technology show that the grid side converter will handle the voltage fluctuations; which is affected by the power fluctuations [2]. The wave power phenomena is more challenging, fluctuations occur for both long and short time scale. Spacing the platforms in accordance to the wave climate is shown to be a proper manner of approaching the power smoothing issue before entering the point of common coupling in the electric network. Results show that effort should be put into research for control strategies and generator control, bearing in mind that the rating of the converter and generator is directly affected by the torque demands. The choice of control strategy, point absorber, and generator should therefore be taken simultaneously, on the basis off economical aspects.