A comparison of the thermohydraulic performance of various rotor cooling techniques for an IPMSM
Electric vehicles are gaining popularity in the transport sector due to growing concerns over climate change. The driving range of these vehicles remains a challenge and higher power densities are therefore needed, which leads to higher heat fluxes. Proper thermal management is crucial to prevent premature breakdown of the wire insulation and demagnetization. Traditionally, the machine is cooled using a stator jacket, sometimes with end-winding jet cooling. These methods are mostly sufficient to cool the stator region, but could be insufficient to cool the rotor region at high rotational speeds where high frequencies cause higher losses in the rotor. As a result, rotor cooling techniques are increasingly proposed, where the use of lubrication oil allows to bring the coolant closer to the heat source due to its dielectric properties. By using oil for cooling and lubrication, there is a possibility to eliminate the water-glycol circuit of the vehicle to increase the power density further. Various state-of-the-art and novel rotor oil cooling concepts are compared within this study based on the thermohydraulic performance for a high-speed permanent magnet synchronous machine. The methods include hollow shaft, rotor jet, direct magnet and rotor jacket cooling in a closed and open loop configuration. The performance of these concepts is simulated using MotorCAD and an in-house developed zonal thermal model which makes use of 2D finite element simulations and analytical methods to construct a three dimensional equivalent thermal network of the complete machine. As a manner of validation a comparison is made between the results of the models for a stator jacket and end-winding cooled machine in a closed loop configuration and it is shown that the steady-state temperatures correspond well. The relative difference in temperature with respect to the coolant temperature between both models is found to be below 0.9%. The magnet temperatures in these validation cases with only stator cooling methods exceed the limit of 150°C, showing the need for rotor cooling. Of the studied rotor cooling methods, hollow shaft cooling does not add a significant improvement in performance, while simulations with hub jet do show an increase in performance. The highest performance is obtained for the direct magnet and rotor jacket cooling methods, where the relative permanent magnet to coolant temperature can be improved by 68% and 44% for respectively the closed and open loop configuration compared to the benchmark, while the hydraulic performance is only slightly lower (less than 10%).
Source (book)
International Heat Transfer Conference 17 (IHTC-17), 14-18 August, 2023, Cape Town, South-Africa
IHTC Digital Library , 2023
p. 1-10
Full text (publisher's version - intranet only)
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Publications with a UAntwerp address
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Creation 19.12.2023
Last edited 20.12.2023
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