Short term sea wave force prediction for feedback control of a wave energy converter

This thesis is about the design of a virtual sensor-based predictor for an offshore, single body, floating sea wave energy converter called ISWEC (Inertial Sea Wave Energy Converter). The pitch rotation of the floater, due to the incoming waves, is combined to the flywheel spinning velocity generating an inertial gyroscopic torque. The Inertial Sea Wave Energy Converter exploits the gyroscopic effect to generate energy. In order to maximize the generated energy, a model predictive control algorithm based on the prediction of future values of the pitch component of the incident wave force, has to be exploited. However, since no sensor is available on the ISWEC for measuring the pitch force, prediction of future values of such quantity is a challenging problem. In this work an original two-stages approach is proposed for the design of the wave force prediction. In the first stage a virtual sensor able to provide real-time estimation of the wave force is designed by applying the set-membership estimation theory. In the second stage, an autoregressive linear filter able to predict future values of the wave force based on the current and past values of the same quantity estimated by the virtual sensor is obtained by means of standard least squares. The designed prediction algorithm has been successfully tested on different data sets obtained from an accurate simulator of the ISWEC prototype.