Usually, a brushless dc motor is commutated. One stator pole is turned-off and the next pole is energized. The windings of a brushless dc motor are distinct seperate pole. This arrangement is the most simple to wind and control, but produces some torque ripple.
A variation of a brushless dc motor uses a slighly different winding. The windings are distributed around the stator to produce a roughly sinusoidal distribution. The stator winding is similar to an ac induction motor. This type of motor is called a brushless ac motor.
A brushless ac motor is driven with ac sinewave voltages. The permanent magnet rotor rotates sychronous to the rotating magnetic field. The rotating magnetic field is illustrated using a red and green gradient. An actual simulation of the magnetic field would show a far more complex magnetic field.
