A variable motor (1) having reduced audible noise. This advantage is
achieved by reducing or eliminating ripple torque by making the individual
phase torques follow a certain profile, so that when the torques are
summed, they are substantially constant. Therefore, the motor (1) back EMF
is used as a reference waveform to control the winding currents to achieve
reduced ripple torque. The back EMF reference is amplified and provided to
the motor windings, and may be derived in a number of ways including use
of sense windings, electronic derivation, and approximation by sensing the
voltage applied to the windings.
