Power take-off concept for wave energy converters based on oil-hydraulic transformer units

A generic oil-hydraulic based power take-off concept applicable to different Wave Energy Converters is presented. This power take-off is developed to have well-adapted characteristics to larger power and low frequency waves and to minimize spring, oscillatory and transient effects of the oil caused by the operation of valves which lead to the damage of pipelines, pumps and accessories. The proposed concept adopts technology already tested in other fields and uses hydraulic transformers and speed control of their secondary drives. Moreover this paper contributes to a better understanding of the implications of using hydraulic transformers in the power take-off system. According to the simulations, approximately 76% of the power take-off hydraulic efficiency might be achieved in the two and most energetic of the three simulated sea state conditions and the ones between these two. The transformer is not used in the less energetic sea state condition just because the use of reactive control is less effective than using damping control. Even in this case the PTO efficiency is 71%. So, using a hydraulic transformer in the power take-off system can be beneficial. (C) 2015 Elsevier Ltd. All rights reserved.