Comparative study of control algorithms for maneuvers of first generation TECs* and two degrees of freedom

From the devices for harnessing the energy of ocean currents (In English, they are denoted as TEC “Tidal Energy Converters”. This term does not englobe all the devices for marine current harnessing), those denoted as first-generation devices are used to obtain energy from underwater currents at depths that do not exceed 40 or 50 m, which configures them as structures supported over the seabed. For the energy exploitation of this resource to be competitive, from a technical and economic perspective, it is necessary to overcome various technological challenges, and to reduce operating costs, focusing the effort on lowering maintenance costs too. Thanks to the implementation of a ballast control system, these generators are equipped with the possibility of automatically changing orientation and depth during emersion-immersion maneuvers, which can reduce these costs. This work presents the dynamic modeling of a device with two degrees of freedom and several multivariable control algorithms, all of them based on a non-linear decoupling matrix, together with the compensation of the loss of buoyancy term in the neighborhood of the free surface. The performance of these controllers is evaluated by simulating the emersion maneuver of a full-scale device, and these results are validated with a small-scale prototype in the Model Basin. Finally, the obtained results under simulation are compared, and experimental validation is presented.