Dynamic performance of a permanent magnet, axial flux, toroidal stator, brushless DC motor

The authors investigate the dynamic performance of an axial-flux, permanent-magnet brushless DC drive. The drive inverter uses six power MOSFETs as switching devices. The motor comprises a slotless toroid as a stator and two discs carrying axially polarized permanent magnet poles as a rotor. The permanent magnets are made of neodymium-iron-boron. A mathematical model of the drive is presented, and two cases of dynamic operation are considered motor start-up and sudden change of the applied voltage. Results obtained show that, for a reliable design, special attention should be given to the fact that the winding inductance is very small in this class of motor and the current peak is almost determined by the winding resistance, which is also very small