A low-order thermal model for monitoring critical temperatures in permanent magnet synchronous motors

Monitoring critical temperatures in electric motors is crucial for preventing shortened motor life spans due to excessive thermal stress. With regard to permanent magnet synchronous motors (PMSM), critical temperatures can occur in the magnets and the stator end winding. While excessive magnet temperatures involve the risk of irreversible demagnetization when operating the motor in flux weakening mode, exceeding the thermal limits of the stator windings can destroy the insulation varnish. As directly measuring temperatures, especially on the rotating part, is costly and thus not applicable with respect to automotive applications, model-based approaches are preferred. In this paper, a low-order thermal model for accurate temperature predictions in the permanent magnets, the windings and the end windings is introduced. The model parameters are estimated solely based on experimental data via a sequence of interdependent identification steps. The model performance is validated by experimental results based on a high-speed PMSM typically used as traction motor in subcompact electric cars.