Declutching control of a wave energy converter

• Published in: Ocean engineering 2009-09, Vol.36 (12), p.1015-1024
• Main Authors: Babarit, Aurélien, Guglielmi, Michel, Clément, Alain H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Declutching control; Energy; Energy of waters: ocean thermal energy, wave and tidal energy, etc; Engineering Sciences; Exact sciences and technology; Fluid mechanics; Fluids mechanics; Hydraulic power take off; Mechanics; Natural energy; Optimal command; Physics; Wave energy converter
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2009.05.006

When hydraulic power take off (PTO) is used to convert the mechanical energy of a wave energy converter (WEC) into a more useful form of energy, the PTO force needs to be controlled. Continuous controlled variation of the PTO force can be approximated by a set of discrete values. This can be implemented using either variable displacement pumps or several hydraulic cylinders or several high pressure accumulators with different pressure levels. This pseudo-continuous control could lead to a complex PTO with a lot of components. A simpler way for controlling this hydraulic PTO is declutching control, which consists in switching on and off alternatively the wave energy converter's PTO. This can be achieved practically using a simple by-pass valve. In this paper, the control law of the valve is determined by using the optimal command theory. It is shown that, theoretically when considering a wave activated body type of WEC, declutching control can lead to energy absorption performance at least equivalent to that of pseudo-continuous control. The method is then applied to the case of the SEAREV wave energy converter, and it is shown than declutching control can even lead to a higher energy absorption, both in regular and irregular waves.