Selection of the flux reference for induction machine drives in the field weakening region

In a conventional rotor flux-oriented (RFO) induction machine drive, the flux reference is usually made proportional to the inverse of the rotor speed for field-weakening operation. It is indicated in this paper, however, that such a variation cannot maintain optimal (maximum) torque capability of the machine over the entire speed range. It is further indicated that a nearly optimal torque capability can be achieved in a stator flux-oriented (SFO) system when the stator flux reference is varied as the inverse of the rotor speed