Study of a Multicoil Electromagnetic Wave Power Takeoff System With Pneumatic Velocity Upconversion Mechanism Targeting Low-Frequency Input

To build efficient and portable wave energy conversion devices, energy-dense power takeoff (PTO) systems are required. Contemporary PTOs developed for wave power stations are focused on the year-round averaged sea condition, leading to undesirable performance under low wave frequencies. Facing the challenge, a multicoil electromagnetic wave power takeoff (ME-PTO) with a pneumatic velocity upconversion mechanism is introduced. The new architecture features a pneumatic cylinder connected to a coiled tube to house a reciprocating permanent magnet for electricity generation, and the designed cross-sectional area differential between the magnet and piston allows for boosting the magnet speed, to deliver more capturable power. Dynamic models for the ME-PTO were established, and a numerical solution from the wave–buoy interaction to the electricity output was developed. A compact 23-mm diameter by 190 mm long prototype was built in the lab and an experimental test platform was constructed for model validation. Initial results of operation between 0.2 and 1 Hz have shown that the power density of ME-PTO can reach 72.4 W/m
³
at 0.4 Hz, and is capable of extracting more wave energy compared to a baseline 50-W mechanical PTO when the incident wave is below 0.2 Hz. Under an incident wave with a peak frequency of 0.31 Hz and amplitude below 0.5 m, the cumulative work density of the ME-PTO can be three times higher than the baseline. Even at higher wave frequencies when the three-phase motor is more efficient, the ME-PTO can still exhibit comparable work density. In addition, performance indicators, such as the yearly energy output density of the prototype, have also been compared to contemporary devices, exhibiting advantages in decimeter-level wave energy extraction.