Comparative study of permanent magnet brushless motors with all teeth and alternative teeth windings

The electromagnetic performance of permanent magnet brushless motors in which either all the teeth or only alternate teeth carry a concentrated coil is compared. Analytical and finite element techniques are employed to predict the airgap flux density distribution, the cogging torque and emf waveforms, and the winding inductances. It is shown that the coil mmf vectors influence the coil pitch and distribution factors, and that this leads to significant differences in both the phase and line emf waveforms and also the self and mutual inductances. Predicted results are validated on two experimental motors.