Multi-resonant feedback control of multiple degree-of-freedom wave energy converters

A multi-resonant multiple degree-of-freedom wave energy converter, comprising:

• a buoy in a water environment having a wave motion, wherein the waves impacting the buoy exert an excitation force with a plurality of excitation frequencies that causes a buoy motion in heave, surge, and pitch directions relative to a reference,
• a heave sensor for measuring the position or velocity of the buoy in the heave direction relative to the reference for a sample period,
• a heave actuator that is configured to apply a control force in the heave direction to the buoy,
• a feedback controller that uses a signal processor to extract a plurality of frequencies, amplitudes, and phases of the measured position or velocity of the buoy in the heave direction, computes a proportional-derivative control for each of the plurality of extracted frequencies, amplitudes, and phases, adds up each of the proportional-derivative controls to provide a computed control force in the heave direction, and causes the heave actuator to apply the computed control force to the buoy to put the buoy heave motion in resonance with the excitation force,
• a pitch actuator that is configured to apply a control torque in the pitch angular direction of the buoy, wherein the pitch and surge motions have natural frequencies and wherein the torque applied in the pitch angular direction and the natural frequencies of the pitch and surge modes are selected to shift energy harvesting from the surge to the pitch mode, and
• a power take-off means configured to convert the mechanical energy of the buoy heave and pitch motions to electrical energy.