ABSTRACT
In alternating current (AC) machines, torque is expressed as the outer product of flux and current vectors. Therefore, to maximize torque the two vectors should be orthogonal. In the direct current (DC) motor, the orthogonality is guaranteed by the brush and commutator action. In AC machines it can be achieved dynamically in the synchronous frame. If the reference frame is aligned with the rotor flux, then the control is called the rotor field-oriented scheme. If the frame is aligned with the air-gap field or stator field, it is called the air-gap field or stator field-oriented scheme. The IM dynamic model mimics the DC motor dynamic model in the rotor flux reference frame in which the roles of the dq-axes current are separated. The d-axis current, functioning as the field current, should be regulated to keep a desired rotor field level.
