Thorough simulations of a three-phase synchronous linear generator, coupled to a simple buoy model, offers a way to estimate the performance of the generator at different ocean sites. The behaviour of the wave energy converter is simulated in a nominal wave condition, as well as in a low power and in a high power wave condition. Finite element (FE) electromagnetic simulations are used to model the generator. The time stepping FE calculations are coupled directly with the equations of motion of the buoy. An annual energy production, based on an authentic wave spectrum, is estimated for the wave energy converter.
Ocean waves represent a power dense source with large quantities of renewable energy (Thorpe 1999). However, wave energy conversion demands a robust technology that can handle the extreme peak loads associated with ocean waves (Vriesema 1995). These constraints and natural variations must be taken into account when selecting and designing an energy conversion system with high total efficiency and long-term durability. Further, if this technology is made cost-efficient and robust enough, we will soon see a commercialized extraction of "stored wind energy" directly from the oceans. There is a growing interest for linear generators in wave energy, and some solutions have been suggested by, for example Mueller (2002) and Pollinder et al. (2000). The present paper is based on a novel wave energy converter (Leijon et al. 2004), involving a linear generator placed on the seabed. The piston of the generator is directly coupled to a heaving buoy by a rope, and the need of gearbox or complex power take off schemes is thus eliminated. The tension in the rope is maintained by springs that pull the piston downwards, see Fig. 1. End stop damper is used to limit the piston motion.