Analysis and optimization of coaxial magnetic gears

Coaxial magnetic gears with permanent magnets have a very simple structure and performance comparable to that of mechanical gears. The paper describes an analytical simplified approach for the analysis and design procedure. The mathematical model is one-dimensional: only the variation of electromagnetic quantities as function of angular position is considered and the permanent magnets are modeled by means of constant currents located at their edges. The resulting magnetomotive force generated by the two rotors is modulated by the distribution of the variable permeance due to the stationary ferromagnetic pole-pieces. The influence of the ratio between the width of the magnet and the pole pitch on the air-gap flux density is also considered. The analytical results are verified by means of a FEM considering the power losses and the torque ripple in order to obtain minimum volumes of the magnets and high torque densities.