Measurement of Rotor Thermal Time-Constant for Permanent Magnet Synchronous Machines

Thanks to their high torque density, permanent magnet synchronous motors (PMSMs) currently represent the most competitive solution in the electrification processes involving transports and energy production. However, it is known how the torque production of such motors is strictly related to the temperature of the permanent magnet (PM), affecting control performance, and efficiency. This issue makes necessary the thermal analysis of the machine, thus requiring the determination of the PM’s thermal time-constant. In this paper, an experimental method for evaluating such a parameter is proposed, allowing high accuracy and reliability of the result. The proposed procedure can be applied to any PMSM type, without being affected by factors such as rotor lamination, shaft, PM distribution. The experimental validation has been carried out on three PMSMs, having different rotor structure, sizes, and voltage/current levels. Experimental results demonstrate the validity of the proposed method.