Electric circuit coupling of a slotted semi-analytical model for induction motors based on harmonic modeling

Abstract

The use of empirically determined coefficients to include the effects of leakage and fringing flux is a large drawback of traditional induction motor (IM) models, such as lumped parameter, magnetic equivalent circuit and anisotropic layer models. As an alternative, Finite Element Analysis (FEA) is often used to determine the magnetic field distribution accurately, although at the cost of a much longer computation time. A good alternative to FEA, both in terms of computation time and accuracy, is harmonic modeling. Therefore, in this work, a previously presented magnetic model for slotted IMs based on harmonic modeling, is extended. The main contribution is the implementation of a direct coupling between the magnetic model and the stator and rotor electric circuit models, both for steady-state and time-stepping approximation of the time dependence. Except for end winding leakage flux, no additional empirical coefficients are required to include leakage and fringing flux effects. The results of the models are validated against FEA results and measurements on a prototype. It is shown that good agreement is obtained for torque prediction, whereas the predicted stator current shows some discrepancy. This discrepancy is caused by saturation of the main magnetic flux path and can be accounted for by hybrid coupling to a model that includes the effect of non-linear soft-magnetic material on the main magnetic flux.