Multi-Timescale Lookup Table Based Maximum Power Point Tracking of an Inverse-Pendulum Wave Energy Converter: Power Assessments and Sensitivity Study

Abstract

A novel, inverse-pendulum wave energy converter (NIPWEC) is a device that can achieve natural period control via a mass-position-adjusting mechanism and a moveable internal mass. Although the energy capture capacity of a NIPWEC has already been proven, it is still meaningful to research how to effectively control the NIPWEC in real time for maximum wave energy absorption in irregular waves. This paper proposes a multi-timescale lookup table based maximum power point tracking (MLTB MPPT) strategy for the NIPWEC. The MLTB MPPT strategy was implemented to achieve a theoretical “optimal phase” and “optimal amplitude” by adjusting both the position of the internal mass and linear power take-off (PTO) damping. It consists of two core parts, i.e., internal mass position adjustment based on a 1D resonance position table and PTO damping tuning based on a 2D optimal PTO damping table. Furthermore, power assessments and sensitivity study were conducted for eight irregular-wave sea states with diverse wave spectra. The results show that energy period resonance and the lookup table based PTO damping tuning have the highest possibility of obtaining the maximum mean time-averaged absorbed power. Additionally, both of them are robust to parameter variations. In the next step, the tracking performance of the MLTB MPPT strategy in terms of changing sea states will be studied in-depth.