The applet shows the cross section, winding scheme and armature current distribution of a two-pole permanent magnet DC machine (left) and a two-pole permanent magnet synchronous machine (right). The mechanical commutator of the DC machine ensures, regardless of the rotation of the armature, that the armature current and the stator field are stationary in relation to each other. The salient pole rotor of the synchronous machine is running with a certain speed. The stator current which forms the torque must also rotate with this speed. This is achieved by a three-phase winding. If all three windings are arranged in 120 degree angles to each other, and three sinusoidal voltages with 120 degree phase shift are applied to these windings, then a rotating magnetic field results. To achieve maximum torque of the machine, one must control the stator voltages in a way that the maximum stator current shows optimum interaction with the maximum of the field of the salient pole rotor.

• Change the position of the commutator of the DC machine. The resulting torque is reduced, and the current component id which does not contribute to the torque, causes additional current stress and losses.
• Change the posistion of the rotor field and/or the stator current distribution of the PMSM. The resulting torque is reduced, and the current component id which does not contribute to the torque, causes additional current stress and losses. When applying dq-control of the PMSM, the current component id will controlled to be zero.