Permanent magnet synchronous motor with axial flux geometry

The machine described here is a synchronous motor with a permanent-magnet rotor in the form of a thin disk sandwiched between two stators. The rotor can be made very light, making it useful for servo drives, since all circumferential flux is carried by the stators and the rotor has no back iron. The magnet material is neodymium-iron boride, making it possible to achieve reasonably high levels of airgap flux density. Because of the shape of the magnets, the rotor magnetomotive force (MMF) has the form of a quasi-square wave, the fundamental of which is considerably in excess of the peak MMF of the wave. The analysis is based on the traveling-wave model of an electric motor and includes saturation in the stator iron and the effects of slot leakage. Results for a laboratory machine are presented and compared with the predictions of the computer model