Numerical and analytical investigations of the water immersion cooling strategy for a permanent magnet synchronous motor

Permanent magnet synchronous motors (PMSMs) experience considerable performance degradation due to the rise in temperature and the resulting partial demagnetisation in the PMs, as well as the shortenings in the insulations' lifetime. To mitigate the temperature of motor components, it is crucial to investigate and continually improve the design of efficient cooling systems. This study implements the water immersion cooling (WIC) concept on a surface-mounted PMSM (SMPMSM), where through comparing its cooling performance with the forced ventilation cooling (FVC), it is indicated that, even at high inlet velocities for the latter, it cannot maintain the temperature below the specified thresholds and the required input electric power to run the ventilation fan will be increased exponentially to compensate for its ineffectiveness. While in the WIC configuration, the winding and PM temperature values remain well below the margins when the heat transfer coefficient of this method is 40% $\%$ higher than the FVC. By incorporating the effect of the cooling process through the heat transfer coefficient, the lumped-parameter thermal network (LPTN) is utilised to study the operation mode of the motor under the mentioned cooling configurations. Besides achieving higher cooling efficiency, the WIC strategy can quickly reduce temperature, which is reflected in the thermal time constant of the cooling method extracted from the LPTN. Consequently, it is demonstrated that up to 35% $\%$ higher than the nominal generated heat, the SMPMSM under the WIC can operate continuously, while for the FVC, the frequent start-stop driving scenario should be employed.