Reduction of the Non-Causal Horizon of the Optimal Wave Energy Converter Control

In our days, wave energy still remains an important resource of renewable energy that has not been yet completely exploited and fully understood. Various prototypes of point absorbers have already been tested numerically and experimentally in wave-tanks or real sea, but only a few of them has reach the full scale prototype stage. For the family of wave absorbers based on oscillating bodies principle, the energy production may be enhanced by motion control. The choice of a particular mode of control remains decisive in the design of point absorbers and is closely linked to the mechanism architecture. It has been shown [1] that the theoretical maximum absorption can be reached by bringing the system into resonance applying a so called “complex-conjugate” control. Several sub optimal control strategies have been derived from this observation, trying to overcome the draw-backs of this method, mainly the non-causality of the optimal control [3]. Non-causality implies that one needs to predict the excitation signal in the near future to optimize the control command. The aim of the present study is to propose a new methodology to reduce the prediction horizon needed to apply a complex-conjugate control. Afterwards, a simplification is made leading to a causal non-adaptive control. In this study, a cylindrical buoy constrained to move in heave only is employed to test numerically the aforementioned control. Numerical comparisons are made under regular and irregular waves with the performance of control based on the classical complex-conjugate method. The new method shows a good energy absorption capacity for a broad range of frequency without having to adapt the control regulator unit to the incident waves.