Reduced lumped parameter thermal model for external rotor permanent magnet motor design

Torque density of electric motors can be increased if the rotor is placed in the exterior. However, this makes heat extraction more difficult. Study of the thermal behavior at the design stage of the machine can be addressed using FEM and CFD methods. However, they are computationally expensive, and consequently not suitable for the evaluation of multiple designs. A short-time consuming lumped parameter thermal model for external rotor permanent magnet synchronous machines is presented in this work. It allows a fast evaluation of multiple machine design options, being suitable for its use in analytical machine design tools. In addition, comparative analysis of the thermal performance of internal and external rotor designs is provided. The developed model is validated by commercial software achieving good results.