Optimal latching control of a wave energy device in regular and irregular waves

This paper describes two methods which can be used to assess the benefit that latching control can bring to the efficiency of wave energy converters. The first method is based on the analytical solution of the equation of motion of the Wave Energy Converter (WEC) in the time domain, using matrix exponentials; it can be used to compute the optimal latching delay. The second one derives from optimal command theory; it is based on a hamiltonian formulation and Pontryagin's maximum principle. A weak modelling is used to describe latching control prior to applying the optimal command theory. These methods are applied to two different WECs. The first one is a generic one degree of freedom wave energy converter, an heaving buoy, and the second one is the four degrees of freedom wave energy converter called SEAREV. It is shown that latching control based on optimal command theory applied to this weak formulation is not fully optimal in regular waves. However, it can be used to generate optimally controlled time domain sequences of the WEC motions in a random sea, and so it provides an answer to the question: what is the maximum benefit latching control could bring to my wave energy device in a random sea? (C) 2006 Elsevier Ltd. All rights reserved.