New Formulation of Wave Energy Converter Control Using Extremum Seeking

Ocean wave energy converter (WEC) requires real-time control to maximise energy conversion. Effective control of wave energy converter is particularly challenging, since the ocean wave is highly uncertain and time-varying. Conventionally, instantaneous control methods are utilised, such as Bang-Bang control and model predictive control with wave prediction, which consequently requires fast controller and responses. In this paper, energy generated in a period of time is regarded as an entirety, and the main wave is considered to impose a periodic excitation force to WEC. Then, it is shown that the optimal power take-off force also follows a periodic function, by optimising which WEC is expected to generate maximum power output. The intriguing relationship among the harvested energy, wave properties and control force is derived in this paper. An extremum seeking control method is implemented to solve this reformulated problem. By extensive simulation results, the effectiveness of the proposed framework and control method is validated, which demonstrates high conversion efficiency comparing to Bang-Bang control and short-horizon optimal control.