An approach to modeling and field-oriented control of a three phase induction machine with structural imbalance

Structurally unbalanced operation of an induction machine typically occurs during emergency conditions. A unified modeling and control approach for a three phase induction machine drive with a particular structural imbalance (one phase open) is developed based directly on the resulting asymmetrical machine structure. With a new stator winding decoupling transformation developed in this paper, the machine (with one phase open) is made equivalent to a two phase machine with perpendicular d-q stator windings having different numbers of turns. Based on this machine model, field-oriented control strategy is developed to guarantee the desired independent control of rotor flux and electromagnetic torque in spite of the unbalanced condition. The method employed may be extended to other types of structural imbalances