A wide range of wave energy converter technologies has been proposed so far. Oscillating body systems are an important class of wave energy converters, which typically harvest wave energy from a single degree-of-freedom response. This article presents a novel 3-degree-of-freedom (heave, pitch and roll) wave energy converter which extracts and converts wave power efficiently. The 3-degree-of-freedom mechanism is invented to absorb and convert wave energy, no matter which direction the waves propagate. The hydraulic power take-off system comprises novel energy conversion devices which can be superposed to realize high-power conversion to produce electricity. First, the power conversion principle of the wave energy converter is proposed, and the kinematics of the 3-degree-of-freedom mechanism is derived. Then, the governing equations of the 3-degree-of-freedom wave energy converter are established. Linear time-domain simulations are performed to calculate instantaneous and mean power outputs. The numerical results show that the rated power absorbed by the wave energy converter is up to 4.2 MW and the efficiency is over 80%. And the power matrix of the wave energy converter is obtained from a range of simulations under different sea states. Finally, directional performance of the wave energy converter is investigated, and the numerical results show that the wave energy converter can operate across a range of incident wave directions, but is most efficient in head, beam and following seas.
Approaching maximum power conversion with exergy-based adaptive wave-by-wave control of a wave energy converter
