High‐torque‐density pseudo‐direct‐drive permanent‐magnet machine with less magnet

Abstract

Magnetic gears, an alternative to conventional mechanical gearboxes, have been extensively studied in the last decade. By combining a magnetic gear and a conventional permanent-magnet machine into one frame, different magnetic-gear-integrated permanent-magnet machines with a high-torque density are obtained, among which the pseudo-direct-drive permanent-magnet machine features both a high-torque capability and a good power factor with an acceptable structural complexity. However, the stator PM array in the conventional pseudo-direct-drive permanent-magnet machine obstructs the magnetic path and reduces the excitation torque due to the coils. Another problem is the large permanent-magnet amount which increases the overall cost. The authors propose a novel topology which has an improved torque capability under the same excitation current with a reduced permanent-magnet amount. The working principles of the proposed machine are analysed theoretically using the linear-material assumption to decouple the permanent-magnet-machine part and the magnetic-gear part. Its performance is then validated by the finite-element method. A comparison study with the conventional topology is conducted to show its merits.