The action of the commutator is to produce a fixed spatial distribution of current directions in the armature conductors independent of shaft rotation. The field created by these currents (armature reaction) is horizontally directed and is represented by the space vector Ia.
The field established by the excitation of the stator poles is directed along the vertical axis and is represented by the space vector λf . The electromagnetic torque may be expressed as
Te = k( Ia x λf ).
Brushless DC Motor
The rotor flux density distribution produced by the permanent magnets is represented by the green space vector Br. A power-processing unit supplies three-phase currents to the stator windings in such a manner that the resultant stator current space vector Is is 90o ahead of the rotor flux vector.
The MMF distribution produced by the stator currents flowing in the stationary three-phase windings is equivalent to that produced by Is flowing in a single sinusoidally-distributed rotating winding whose magnetic axis lines up with Is as illustrated in this animation.[/et_pb_text][/et_pb_column] [/et_pb_row] [/et_pb_section]