Direct field-oriented control of induction motor with iron-core loss compensation and robust parameter identification

This paper focuses on an accurate flux and torque control strategy of a direct field-oriented induction motor drive incorporating both iron-core loss compensation and robust parameter identification. The fundamental control algorithm is based on the direct field orientation, which essentially requires rotor flux estimation using several motor parameters and detection of line currents and rotor position. In order to suppress the flux estimation error caused by the parameter mismatch, the magnetizing inductance and the rotor resistance are identified insensitively to the stator resistance by using instantaneous reactive power. However, due to a model mismatch associated with the equivalent iron-core loss resistance, neither the field orientation nor the parameter identification can be achieved as is expected, which mainly results in degradation of flux and torque control accuracy. This paper describes characteristics of the motor parameters precisely measured under various operating conditions, the influence of iron-core loss resistance on the field orientation and the parameter identification, and a compensation technique to obtain higher controllability than conventional field-oriented control techniques. Effectiveness of the proposed technique has been examined through experimental tests as well as computer simulations, and the absolute accuracy and linearity of the motor torque has been improved as a result