*5.2. Thermal Model*

An LPTN model of the IM was used as the thermal model. This was built in Motor CAD using the geometry and winding data of the exemplary machine. The LPTN created by Motor-CAD® was extracted and imported into MATLAB®. The thermal parameters and the LPTN of the machine are explained in [24]. The LPTN is solved in Matlab using the modified nodal potential analysis and the Backward Euler method.

Two options can be used to calculate the electromagnetic losses used as input for the thermal simulation. Both options are equivalent in their results. First, in each step where the losses are updated, the electromagnetic model can be calculated with the actual temperatures of the stator winding and the rotor cage. This implies a high computational effort, especially for the numerical models, since the FE simulation must be performed at each step. On the other hand, for a given stator winding and rotor cage temperature, the machine can first be calculated with the selected model and the influences of the temperature changes on the losses can be determined using the scaling laws of IM described in [8,22,25,26]. This reduces the computational effort while maintaining the quality of the calculated losses, as shown in [8,22,25,26].
