Evaluation of multiphase brushless permanent magnet (BPM) motors using finite element method (FEM) and experiments

This paper analyzes the behavior of 2-phase, 3-phase, and 5-phase brushless permanent magnet (BPM) motors when supplied by suitable variable speed drives. The objective is to evaluate the suitability of these BPM motors for different applications. Nonlinear finite element method (FEM) is used for studying the flux density at various points of the machines and for calculating the developed static torque. The effect of the number of phases on the developed torque and the flux distribution in the back-iron and stator teeth is studied. Also, the effect of different current excitation waveforms on the developed electromagnetic torque generated in 2-phase, 3-phase, and 5-phase BPM motors at full load is studied. Further, dynamic simulation is used to predict the torque ripple in these BPM motors. Simulation results are verified by experimental results obtained from 2-phase and 3-phase BPM motors. It is shown that for the same amount of copper loss, the 2-phase BPM motor is more cost effective as it gives higher average torque as well as peak torque. However, it generates deeper notches in the developed torque, Iron utilization is better in the 5-phase BPM motor. The peak back-iron flux density remains the same as in the 2-phase and 3-phase BPM motors.