Design of an electrical machine for a wave generation system

Abstract

Utilisation of renewable resources is constantly becoming a necessity in the power generation industry. For countries like Malta, whose rural areas are limited but possess a larger accessibility to coastlines, wave energy conversion could be an alternative way of power generation. This led to the design of new concepts while improving those which are already in operation. A prototype wave energy converter of the wave activated type was made available to the University of Malta. A new power take off system to replace the existing hydraulic one was required. Thus, given the type of motion exerted by the waves, it was decided to design a linear generator. The design needs to operate efficiently in the local conditions so data analysis of actual site data was an important step in the machine design optimization process. The site data was gathered through dedicated instruments that were anchored at the selected location. Based on these results it was concluded that due to the way the prototype converter interacts with the waves it does not result in a significant amount of power absorbed and will not operate efficiently in the local wave conditions. So a point absorber converter was suggested. The latter can still operate with a linear generator. This study also included the analysis of the dynamic motion of the proposed structure as it heaves with the waves' motion. Optimisation of the buoy's dimensions was carried out through results obtained from WAMIT. This is a commercial code which simulates hydrodynamic loads on offshore structures. Based on this analysis the linear generator could then be designed through simulations that were carried out in ANSYS Maxwell and ANSYS Simplorer. The model was designed for waves that yielded the maximum power throughout the year however it was necessary that the machine will give a reasonable performance when hit by slower waves. A 4-, 8- and 16-pole tubular linear machines were simulated whose results were then compared to each other. Through this analysis the 16-pole design resulted in the best performance, especially at low speeds. Simulation results were initially compared for fixed speed conditions. Later simulations with variable speed conditions were also carried out so as to represent the wave' s motion. A flat equivalent of the 16-pole tubular linear machine was also simulated for comparative reasons. The study carried out was part of the Blue Ocean Energy Project through the MCST R&I 2010-024 funding. The purpose of the Blue Ocean Energy project was to verify whether the proposed full scale pilot project is well-founded and is likely to meet the needs of its beneficiaries in terms of reliable and competitive C02 neutral wave energy off shore Malta. However this work simply deals with the work carried out for the replacement of the current power take-off system on the provided 1: 10 scale model converter.