A Dual-Stack Coaxial Magnetic Gear for a Wave Energy Conversion Generator

This article presents the electromagnetic and mechanical design and analyses of a 7.67:1 gear ratio magnetic gear (MG) for a wave energy converter demonstrator. A 2-D and 3-D magnetostatic finite-element analysis (FEA) was conducted to maximize the mass torque density. To increase torque without increasing the diameter, a unique dual-stack rotor topology was used along with a 12-segment per pole-pair inner rotor Halbach array and a four-segment per pole-pair outer rotor Halbach topology. The eddy current loss within the MG was mitigated by using laminated magnets and low-loss electrical steel. The experimentally tested MG had a peak torque of 1796.8$\text{N}\cdot \text{m}$, which corresponds to an active region volumetric and mass torque density of 221.1$\text{N}\cdot \text{m}$/L and 105.74$\text{N}\cdot \text{m}$/kg, respectively. The efficiency at rated speed and maximum torque was measured to be 95%. A new in-plane eddy current loss mechanism was identified as being a primary reason for the measured electrical losses being higher than the initially calculated one.