In some applications such as Electric Vehicles (EVs), the overload operation of electric machines is necessary to comply with the performance requirements. The torque/power profile of EVs requires the electric machine to generate high torque/power that can be several times larger than its rated values. The high demand for torque/power can lead to excessive temperature rise causing demagnetization of permanent magnets or insulations deterioration [1]. To avoid these problems, the thermal performance of cooling systems must be considered as a key design factor for electric machines.The extreme overload demand and need for compact packaging limit implementation of air-cooling systems for EV’s electric machines. On the other hand, while fluid-based cooling systems offer high thermal performance, occupying a relatively high volume and consuming extra electrical energy restrain their employment as a favorable cooling solution.&nbsp;In recent years, as an alternative to air cooling and fluid-based cooling systems, increasing attention has been paid to cooling systems based on Phase Changed Materials (PCMs). PCMs are able to store the thermal energy generated by heat sources and release it to air or a heat exchanger through their phase state changing [2]. This process enables realizing a high thermal performance cooling system in a relatively smaller volume than active cooling systems without the need for electrical power. These advantages satisfy the requirements of high density and efficient cooling systems for EV’s electric machine applications.In this study, thermal performance and design criteria of passive cooling systems based on PCM for electric machine applications have been investigated. The cooling system uses a metal-based PCM for heat transfer and temperature control of electric machines under excessive overload operation points. Metal-based PCMs have higher melting temperatures and higher thermal conductivities compare to oil-based PCMs. The fluid flow and transient heat transfer are simulated using the numerical finite element method. The accuracy of the numerical results obtained from the simulation of the phase change process of PCMs has been evaluated by implementing validation methods and a good agreement has been observed. The sensitivity of numerical results to the number of computational elements and the time step size has been analyzed. According to the results, using PCMs, the operating temperature of the electric machine under a given transient excessive peak power demand maintains within the allowable range for more than 600 seconds. This meets the overload demands of the standard dynamic EV&nbsp;driving cycles. Investigation of the effect of the chamber arrangement of PCMs shows that the arrangement has a significant effect on the cooling performance of PCM-based cooling systems. As the number of channel turns filled with PCM increases, the amount of time allowed to maintain the temperature within the allowable range has increased significantly.

Numerical Thermal Performance Investigation of an Electric Motor Passive Cooling System Employing Phase Change Materials

Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2021/volume/84874

ASME 2021 Heat Transfer Summer Conference (SHTC2021)

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