Calculation of load-dependent equivalent circuit parameters of squirrel cage induction motors using time-harmonic FEM

Purpose - The purpose of this paper is to define a time-efficient numerical procedure for the extraction of load-dependent equivalent circuit (EC) parameters of induction machines. The parameters are determined for every operating point, thus their variation due to skin effect and material saturation under arbitrary load condition is taken into consideration. Design/methodology/approach - Two methods are presented and compared. The first one is based on the numerical simulation of the standard measurement process, yielding an EC with constant parameters. A time-harmonic finite element analysis is applied in the second method to calculate the load-dependent EC parameters. Material linearization and the superposition principle for the magnetic flux are employed to define the leakage inductances. Findings - A distinct load dependence of all EC parameters has been proven as well as the clear disparity between stator and rotor leakage inductances. These effects can only be taken accurately into account by the EC obtained by the second numerical procedure proposed. Originality/value - The presented method successfully overcomes typical problems of the measurement process and of the standard numerical procedure for EC parameter estimation, thus the obtained EC parameters are load-dependent while the physical interpretation of the variables and parameters remains straightforward. Hence, the paper of the internal machine variables is enabled.