Development of low cost multi-phase brushless DC (BLDC) motors with unipolar current excitations

This paper evaluates the performance of different brushless DC (BLDC) motors when excited with unipolar currents. Exciting the BLDC motor with unipolar currents reduces the cost of the drive by decreasing the number of switches used in the converter. Two-phase, three-phase, four-phase and five-phase BLDC motors are considered in this study. 2-D finite element method (FEM) is used to obtain the back-EMF waveforms of the motors, which are then used to calculate the dynamic torque outputs with different current excitations. It is shown that by a proper combination of slots/pole ratio of the machine and unipolar current excitation waveform, lower torque ripple can be obtained than with the conventional 3-phase, 12-slot BLDC motor with 120/spl deg/ bipolar current excitation.