Performance comparison of sinusoidally-fed PM BLDC motors having different rotor topologies

Sinusoidally-fed permanent magnet brushless dc (PM BLDC) motors are supposed to develop effectively ripple-free dynamic torques. This is done by having a sinusoidal flux density distribution in the airgap followed by a rotor position dependent sinusoidal excitation of the phase windings. There are different rotor topologies used in these motors. In this paper, five types of generally used rotor topologies are considered with the same volumes of the permanent magnet materials and rotor core laminations, and the performance of the motors for the same stator geometry and winding excitations are compared. It is observed that the bread-loaf rotor topology gives better performance in terms of the developed torque, torque ripples, cogging torque, and near-sinusoidal back-EMF profile. Also, the motor performance is compared for various operating load angles and it is observed that in general, the optimum load angle for all these rotor topologies will be in the vicinity of 60° (electrical), which provides minimum torque ripple and minimum distortion in back-EMF waveform.