Real-time implementation and validation of optimal damping control for a permanent-magnet linear generator in wave energy extraction

To accommodate ocean-wave energy extraction in a wide operating range of sea-states, a nonlinear model predictive control (NMPC) methodology was applied to a lab-scale dual coaxial-cylinder wave-energy converter (WEC), coupled with a permanent-magnet linear generator (PMLG) as the power take-off (PTO). The paper focuses on the experimental implementation of the optimal damping control of the PMLG as guided by the NMPC process, which yielded intermediate values of damping subjected to prescribed damping capacity. This damping behavior was implemented electronically in the coupled PTO-WEC system by employing a solid-state relay (SSR) with pulse-width modulation (PWM) technique so as to mimic analog current flow. The effectiveness of the combination of SSR and PWM was demonstrated. Successful real-time lab-scale testing in regular and irregular waves was experimentally confirmed. Peak values of energy capture and a broadened bandwidth were favorably improved compared to those obtained using just constant, non-time-varying damping control.