2. The DC machine action model

Modeling and analyzing the torque expression of a separately excited d.c. machine are pedagogically essential to understanding the concept of vector control of an asynchronous machine.

In fact, the magnetic state of the DC machine is naturally described in a two-phase (d, q) reference frame.

(d: direct axis, q: quadrature axis)

As shown in figure 1 , the machine consists of three windings: the armature winding on the rotor, a quadrature field winding on the stator and a compensation winding for the armature magnetic reaction.