Improving the Thermal Conductivity of Form-Wound Litz-Wire Windings for Slot-less Machines

The power density of electric motors for aircraft propulsion is maximized by optimizing the electrical and magnetic loading and operating at high speed. Maximizing the current density without constraining the speed (and, consequently, the frequency) and the working magnetic field would significantly improve the power density. However, this would increase resistive losses in the winding which need to be removed through heat conduction. Thus, improving the winding thermal conductivity is an essential piece of motor design, especially for slot-less machines. This paper focuses on the comprehensive process of theoretically and experimentally evaluating the equivalent thermal conductivity for Litz-wire configured windings made with a single turn and multiple turns for slot-less permanent magnet synchronous machines. A detailed experimental procedure for various winding designs will be introduced, discussed, and confirmed through a bench test with an assessment of the results. The evaluation and comparison of windings formed with various resins are also performed to demonstrate potential thermal conductivity improvement through appropriate winding design.