Vector control of an induction motor for the field weakening region with tuning of the magnetizing inductance

Abstract

Above base speed, the flux level must be reduced in inverse proportion to the actual rotor speed. Then the magnetizing inductance is varied by rotor flux reference. In this region, if there is incorrect magnetizing inductance value in the vector controller, it is difficult to properly obtain the magnetizing current and the decoupling terms. The improper magnetizing current decreases the voltage margin, so that makes torque response unstable. Also, improper decoupling terms make voltage reference incorrect. The torques in the stator and rotor flux reference frame have been calculated. If the magnetizing inductance is correct, two torque values are the same. Therefore, if two values are different, the controller has different magnetizing inductance from that of the actual motor. This paper presents the new tuning scheme of the magnetizing inductance by comparing two torque values. The rotor time constant tuning and magnetizing inductance tuning scheme make the vector control system properly operating on the wide speed range. Especially, the improved system performance in the field weakening region by applying this scheme is illustrated. Computer simulation and experimental results demonstrate the efficacy of the proposed scheme.