Analysis of a Novel Multi-Tooth Flux-Switching PM Brushless AC Machine for High Torque Direct-Drive Applications

A three-phase, multi-tooth flux-switching permanent magnet brushless ac machine is analyzed, its electromagnetic performance, viz., the phase flux-linkage and back-EMF waveforms, the self- and mutual-inductances, the cogging torque, the electromagnetic torque, and the torque-current characteristic, are predicted by 2-D and 3-D finite-element analyses and validated experimentally. Compared with a conventional flux-switching machine, a multi-tooth machine requires a significantly smaller volume of magnet material, since only half the number of permanent magnets is required, and it exhibits a higher torque density at low excitation currents as well as a lower torque ripple. However, since it saturates more quickly as the current is increased due to the higher armature reaction, and at very high electric loadings its torque capability is lower than that of a conventional flux-switching machine.