Improved torque response by tuning of the magnetizing inductance under field weakening operation region [of induction motors]

In this paper, the stationary and rotating tangent torque angles of an induction motor have been calculated for exact position information of the rotor flux. If the rotor time constant is incorrect, two tangent values are different. Therefore, using this difference of two values, the correct slip gain is established against the variation of parameters in whole speed range. In spite of the correct slip gain, if there is an 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 it makes torque response unstable. Also, the improper decoupling terms make the voltage reference incorrect. Stationary and rotating reference frame torques have been calculated. If the magnetizing inductance is correct, the two torque values are same. Therefore, if the two values are different, the controller has a different magnetizing inductance from that of the actual motor. This paper presents a new tuning scheme of the magnetizing inductance by comparing two torque values. The proposed rotor time constant tuning and magnetizing inductance tuning schemes make the vector control system operate correctly over wide speed ranges. 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.