The potential benefit of a tidal compensator for the wave energy converter (WEC) studied at Uppsala University is significant since the changing sea level will otherwise reduce the efficiency of power production. A tidal compensation system prototype that adjusts the length of the buoy line according to the change in the water level relative to the seafloor is being developed. The DC motor of the compensation system is powered by a hybrid power system composed of a small wave energy converter and a PV solar cell system. The control system is designed to keep the average power consumption reasonably low while adjusting the position of the roughly 10 ton translator inside the generator. An experimental setup in a lab environment has been completed: a control strategy now has been developed and power consumption measurements has been carried out. The results show that the compensation system is able to operate with an estimated load of 10 tons, the combined load of the WEC translator and the buoy line.
Various types of wave energy converters (WECs) have been developed and tested (Titah-Benbouzid & Benbouzid, 2014; Wang, Isberg, & Tedeschi, 2018). The WEC developed by Uppsala University is based on the concept of heaving point absorber where the energy production benefited from the heave motion of the buoy carrying a translator inside the generator on the seafloor. The status update on the WEC development at Uppsala University until 2015 is reported in (Parwal et al., 2015). Several approaches have been implemented to optimize the performance of the WEC, e.g. (Engström, Eriksson, Isberg, & Leijon, 2009; Engström, Kurupath, Isberg, & Leijon, 2011; Sjökvist et al., 2014). An approach to optimize the power production is to adjust the line connecting the buoy to the translator. This is achieved by using a winch system placed in the WEC's buoy which connects to and regulates the line to the generator at the seafloor. The change in mean sea level shifts the position of the translator from the center in the generator. The first prototype of the compensator was developed for sea level variation of 1m (Castellucci, Abrahamsson, Kamf, & Waters, 2015). This paper presents the control system of the new compensator, designed for sea level variation of 8 m, and shows the results obtained from test in the lab environment. Figure 1 shows the main parts of a Uppsala University WEC and illustrates a possible installation of the compensator inside the buoy.