dc motor consists of two parts i.e. rotor and stator. stator consists of field winding while rotor (also called armature) consists of armature winding. when both armature and field are excited by dc supply, current flows through windings and magnetic flux proportional to the current is produced. when the flux of field interacts with the flux of armature, it results in motion of the rotor. armature control is the most common control technique for dc motors. in order to implement this control, the flux is required to be kept constant. to this aim, either the stator voltage is constant or the stator coils are replaced by a permanent magnet. in the latter case, the motor is said to be a permanent magnet dc motor and is driven by means of the only armature coils.