FIELD-ORIENTED CONTROL OF INDUCTION MACHINES EMPLOYING ROTOR END RINGCURRENT DETECTION

The usual method of induction motor torque control uses the indirect f ield orientation principle in which the rotor speed is sensed and slip frequency is added to form the stator impressed frequency. Unfortunat ely, the rotor resistance varies as the motor heats up under load ther eby changing the rotor time constant which has a deleterious effect on the torque response. In this paper two new field oriented control sch emes are presented which employ rotor end ring current detection and t hereby remove the dependence of the controller accuracy on temperature so that the controller is entirely independent of rotor time constant variations. The field orientation schemes do not require an increment al encoder for rotor position sensing. The motor torque can be accurat ely controlled even down to zero speed operation.