Pedro Beirão

Modelling and Control of a Wave Energy Converter

Abstract This work addresses an offshore oscillating water column for producing electricity from sea waves. It describes the modelling of this device and the study of control techniques that could improve energy extraction. Optimisation techniques applied improved the device performance for a wide number of sea states. A control strategy was developed with the objective of improving the quality of the energy absorbed by the device. This proved to be effective. In a later stage of this work, some experiments considering a variable pitch Wells turbine were performed with the objective of applying phase and amplitude control: it was possible to prove the possibility of obtaining a resonant response to a sinusoidal wave with a frequency different from the devices natural frequency.

ISWEC control tuning: lessons learned

ISWEC (Inertial Sea Wave Energy Converter) is a floating device that exploits the gyroscopic reactions provided by a spinning flywheel to extract power from sea waves. The first sea demonstrator has been deployed in August 2015 at the Island of Pantelleria, Italy. Starting from experience gained working in the real sea environment, some observations about the control are presented. The control of the device aims to exploit all the available control parameters in order to maximize power generation. At first the tuning of PTO control law is analysed and then the additional control degree provided by the gyro speed is considered too. A new developed control technique is briefly introduced. It consists of an application of a standard linear quadratic regulator coupled with a properly designed nonlinear static term. A comparison of previous and new control techniques is presented, proving that the new control is able to insure almost the same power absorption performances while reducing the number of control parameters to be tuned

Tuning a linear quadratic regulator for point absorber wave energy converters

A Wave Energy Converter deployed in Italy uses Proportional—Derivative control to optimise its Power Take-Off system. Different controllers were obtained for different sea states, but this cumbersome process takes a long time. This paper explores the alternative possibility of a time invariant control law (a Linear Quadratic Regulator) based upon optimal control theory, relying upon simulations of a simpler heaving point absorber