Stability control of a floating hybrid renewable energy generation system applying multivariable cooperative control techniques through a linear quadratic integral controller

This work presents, from two different points of view, the simulation of the behavior of a floating hybrid system consisting of a spar-buoy wind turbine type “OC3-Hywind”, to which two marine current turbines have been added. Initially, the response of the floating hybrid system is presented under the simulation of weather conditions that could be found in the Strait of Gibraltar; in this case, the floating hybrid system behaves naturally. Based on the analysis of these preliminary results, a righting control system has been designed, with the aim of minimizing the heeling angle of the floating hybrid system but maximizing energy production. In this way, the goal is to try to reduce structural loads and the wear of materials with maximum energy efficiency. The righting control system has been designed by applying cooperative control techniques using a multivariable LQI (linear quadratic integral) controller. The behavior of the floating hybrid system under these weather conditions has been simulated using the FHYGSYS (floating hybrid generator systems simulator) tool developed in Matlab® code. The design process of the time-domain LQI controller, which controls a complex system such as the one described in this work, is explained in detail and has also been developed using Matlab® code. The results confirm the possibility of reducing the heeling of the floating hybrid system but sacrificing part of the electric power generation. Based on the results, the designed righting control system works as a cooperative control system, presenting operational robustness to variations in wind speed and extreme weather conditions.