Forgive me - your punctuation is slightly confusing, but the principle of using an alternator as a motor is very simple, once you have a source of 3 phase AC*.
The field coil will follow the rotating field provided by the stator coils, once it is suitably energised with DC, so the alternator works in reverse, becoming a 3 phase motor.
You would probably need to limit the current flowing in the stator coils because their impedance would be very low, but this could all be done in the GCU.
*On most airliners the APU supplies this.