Damping Profile Research for Corpower Ocean's Wave Energy Converter

Abstract: With increasing energy demanding and greenhouse gases from fossil fuel, the need to develop new ways to convert energy in sustainable methods is becoming more and more urgent. Corpower Ocean AB designed a point absorber type wave energy converter to harvest energy from surface wave. To maximize the energy output, phase and amplitude control of the converter are needed. Falnes and Budal proposed latching around 1980s which could deliver almost perfect phase and thusly boost power output, however, the peaky machinery force and power output result from it’s discontinuity remained a problem. A continuous phase control method using a negative spring called WaveSpring which further increased power absorption was recently proposed by Jørgen Hals Todalshaug. Meanwhile, there are more and more promising results indicate it is possible to predict the wave in coming seconds. Corpower Ocean’s wave energy converter implements the WaveSpring approach, further more, flywheels are used in the system to increase damping capacity and in the mean time work as a temporary energy storage. In this thesis project, an optimized damping profile making use of wave estimation applying wave to wave control was researched. Optimal damping during regular waves with certain wave height and wave period were first calculated by approximating the wave energy converter using linear oscillation theories. They were then used in wave to wave control by predicting and discretizing irregular ocean waves. The damping was first implemented using only generator and then with a combination of generator and flywheel making use of flywheel equivalent damping and inertia calculated from Fourier decomposition. Damping profiles were tested in Corpower Ocean’s simulation model, simulation results showed that the specific wave to wave control significantly increased energy output, and using the combination of flywheel and generator was confirmed effectively decrease the maximum torque requirement of the generator while maintain high energy output.