Research on an innovative magnetic helix hybrid excitation rotary generator with remarkable power density and efficiency for wave energy conversion

Aiming at the limitations of direct drive wave energy conversion (DD-WEC), especially the poor power density, low energy conversion efficiency, and a large volume of linear generators (LGs), a novel magnetic helix hybrid excitation rotary generator (MH-HERG) with the higher power density and higher energy conversion efficiency is proposed. The proposed MH-HERG can convert linear motion into rotary motion without contact with a hybrid excitation magnetic screw (HEMS) unit, so it has high energy conversion efficiency. Furthermore, a new quasi-Halbach magnetization array is used in the proposed MH-HERG to increase its power density and allows a hybrid excitation method to be used to make the thrust adjustable to further improve power density. The analytical solution model is established to derive the calculation equations of air gap flux density, which are validated through the finite element simulation. Arc-shaped permanent magnets (PMs), instead of tile-type PMs, are designed to weaken cogging torque and harmonic content in proposed MH-HERG's no-load back electromotive force (back-EMF), thereby improving output power quality. Finally, the prototype is built and an experiment is conducted to ascertain the effectiveness and superiority of the proposed MH-HERG which has increased power density by 4.4 times and energy conversion efficiency by 3 times compared to existing LGs.