Robust gain scheduling control for wave energy conversion

Enhancing the power performance of wave energy converters is undoubtedly a step required to reduce the cost of energy from this source of renewable energy, thereby making it competitive to other sources of renewable energy. Increasing the power absorption can be achieved by utilizing smart and advanced control algorithms. There are theories for a variety of advanced control algorithms, but few have proved stable and reliable for real applications. An often used, and robust method for practical applications, is to apply a simple gain scheduling controller where the control gains are parameterized in function of the sea state, and not at wave-by-wave level. This paper presents a wave-by-wave adaptive controller, which has proven a robust method that can increase the power absorption performance. The use of the wave by wave adaptive controller is achieved by the identification of the instantaneous fundamental frequency in real time. One numerical procedure to achieve this frequency is using non-linear Kalman filters. But the pitfall of these non-linear filters is their sensitivity to the parameter tuning, which decreases practical usability, reliability and robustness. This paper focuses on two complementary topics. The first topic will tackle the implementation of a reliable filter for the identification of the instantaneous fundamental frequency using a particle filter. The second topic will demonstrate the implementation of the wave-by-wave gain scheduling controller. The case study is a scaled absorber of the Floating Power Plant wave and wind energy converter.