Optimal Control of Floating Oscillating Water Column Wave Energy Converters

In recent years, there has been a growing focus on wave-to-wire (W2W) control of wave energy converters, aiming to fully harness the potential of wave energy devices. The W2W optimal control problem presents significant challenges in the marine energy field due to the complexity involved in developing detailed mathematical models for power take-off units and other supporting systems. In this context, oscillating water columns (OWCs) stand out as devices with the most robust technology, with all the power take-off equipment implemented above the water line and no need to move excessively to generate energy, unlike other point absorbers. The modeling of these systems is straightforward, as they have been extensively researched across multiple engineering fields, and both empirical data and performance maps are readily available. This paper investigates two simple optimal control formulations for OWCs. The first formulation is turbine efficiency maximization (TEM) control, and the second is W2W control. Both control methods are implemented in the presence of mooring systems, nonlinear excitation, and nonlinear hydrostatic forces. The study then compares the two control methods and highlights the impact of considering the entire power conversion chain within the control method on the performance of the turbine and generator. The results from this study show that a 30% increase in electrical power generation is expected when a W2W approach is implemented compared with the more traditional TEM approach. The TEM model used in this study is publicly available at: WEC-Sim Applications GitHub repository.