Control Strategies for the ISWEC Wave Energy System

The control of the motion of a Wave Energy Converter (WEC) is a key factor for its wave power extraction capabilities. The goal of this paper is the optimization of the power performance of the ISWEC Wave Energy System. The ISWEC is a WEC exploiting the precession of a gyroscopic system to drive the Power Take-Off (PTO). The control of the device aims at exploiting all the available control parameters in order to maximize the extracted power. At first the tuning of PTO stiffness in addition to PTO damping is analysed and then the additional control degree provided by the gyro speed is exploited, too. Application of multi-parameter control strategies, especially when including a reactive component, can however be highly demanding from both the mechanical and electrical standpoint. In order to obtain a sustainable operative condition for the system it is necessary that the applied control avoids excessive oscillation and velocity within the PTO torque and power rating constraints. In this paper a control strategy that inherently takes into account such limitations and consequently adapts itself to the incident waves proves to significantly improve the system performance. In order to test such an adaptive control technique an ISWEC device with rated power of 3 kW and working in the Alghero site is here considered and tested with different floater configurations to derive convenient design trade-off for the considered application.