Evaluation of High Performance Rotor Cooling Techniques for Permanent Magnet Electric Motors

A thermal analysis of an interior permanent magnet machine using a lumped parameter model is presented, with the objective to evaluate several rotor cooling techniques for electric vehicle applications which are needed in order to achieve higher power densities. Two of the selected rotor cooling techniques involve cooling of the shaft by pumping a liquid through a channel in the shaft and by implementing a rotating heat pipe. The third selected rotor cooling technique is accomplished by pointing liquid jets towards the hub of the rotor. The lumped parameter model and implementation of these newly modeled cooling techniques are described. From the temperature distributions of the electrical machine resulting from water jacket cooling in combination with the different rotor cooling techniques, it was revealed that when the rotor of an electrical motor contains a hub, shaft cooling methods are ineffective. Rotor jet cooling however resulted in the most effective cooling approach to minimize permanent magnet temperatures.