Collective control in arrays of wave energy converters

A Collective Control is developed in this paper for arrays of Wave Energy Converters (WECs). The proposed controller applies a Proportional-Derivative feedback control law for each WEC with the optimized controller gains. A surrogate model, composed of only mechanical elements, is adopted to replace the hydrodynamic model during the optimization process. An indirect exterior penalty function approach is implemented to handle the constraints on the displacement and control. The weight of the penalty function is updated in subsequent iterations in the Sequential Unconstrained Minimization Technique. A numerical simulation is first conducted for identification of the surrogate model parameters. With the control gains optimized based on the surrogate model, the energy conversion is compared for three models: the surrogate model, a model that uses a boundary element tool to compute the hydrodynamic forces, and a simulation using AQWA. The results show a good agreement of the energy conversion among the models. Finally, the performance of the surrogate model is analyzed. It is shown that the proposed controller maximizes the energy conversion of the entire WEC array while satisfying the constraints. Moreover, the surrogate model can replace the hydrodynamic model to predict the system behavior with adequate accuracy and more efficiency.