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

Two methods to determine the equivalent circuit parameters of squirrel cage induction motors (IM) are presented and compared. The first one is based on the time-harmonic finite element method (FEM) simulation of the measurement process (short-circuit and no-load test), yielding an equivalent circuit with constant parameters. In addition, the time-harmonic FEM is applied in the second method to calculate the load-dependent equivalent circuit parameters of squirrel cage IMs. Here, the material properties in a two-dimensional finite element model of the induction machine are linearized in each operating point and the superposition principle for the magnetic flux is applied to define the leakage inductances. Hence, the parameters are calculated for every operating point separately, thus the variations of the parameters due to skin effect in the rotor bars and due to material saturation under arbitrary load condition and rotor speed can be taken into account.