PM brushless DC (BLDC) motors should be fed by
square-wave currents synchronized with the back emfs to
develop a constant torque with the required value. In practice,
phase inductances and limited source voltage produce non ideal
square-wave currents and unbalanced phase currents during
commutations. Such phenomena affect the torque developed by
the PM BLDC drives by deviating its value from the requested
one and by giving rise to torque ripple. In this paper, an
analytical study of the torque characteristics, namely motor
torque and torque ripple, of PM BLDC drives is carried out as a
function of the motor speed and is supported by experimental
data. Torque characteristics are expressed in terms of a quantity
distinctive of the motor, thus giving a generalized formulation to
the results.
