Thermal modelling of an axial flux permanent magnet machine

The imperative for conserving energy highlights the need for considering the more widespread implementation of higher efficiency electric machines such as the axial flux permanent magnet (AFPM) machine. Because of their compact geometry and high power densities, the cooling of these machines is important. The objective of the paper is to present the basic architecture of an 300 kW rated at 2300 rpm machine and the basis on which it was thermally modelled, thus allowing a designer to predict transient temperature responses for different design variables and operating conditions. The theoretical equations on which the fluid and thermal model is based are given and include the option of using a heat pipe. The system of equations constituting the model is solved using a computer program. Typical results are given and a sensitivity analysis is undertaken in which changes in rotor–stator clearance and magnets widths, and rotational speeds could be investigated. A number of conclusions are drawn. Increasing air flow rate beyond 0.5 kg/s does not significantly reduce maximum operating temperatures, re-entry of outlet air should not be allowed to re-enter the machine and gap ratios, magnet widths and emissivity have a relatively small effect on the maximum operating temperatures.