Transient torque response improvement in presence of axial saturation due to skewing of rotor slots in induction motors

This paper proposes two new techniques to improve the transient torque response in presence of axial saturation due to skewing of rotor slots in induction motors. The effect of skew is to cause significant air-gap flux path saturation at one axial-end element of the rotor, loss of flux, and, consequently, of drive performance. The induction motor operations with variable q-axis current command during rapid speed changes are studied with a 3 dimensional dynamic magnetic reluctance model (DMRM). The new techniques for compensation of flux loss regard the indirect rotor flux oriented (IRFO) control. The first technique is based on a modified omega slip calculator, and the second one on a modified adaptive i-omega estimator. The paper proves the effectiveness of the two techniques and also shows the stator flux oriented sliding-mode (SFO-SM) control is low sensitive to the rotor bars skew effect and ensures high performance, without any accurate parameter tuning