Modeling of end-space convection heat-transfer for internal and external rotor PMSMs with fractional-slot concentrated windings

Modeling of convection heat-transfer at the end-windings for thermal networks using lumped-parameters has been widely discussed in the literature. Unfortunately, the resulting coefficients are highly influenced by the end-winding shape, the area in the vicinity of the end-windings, the cooling method of this region (if any), as well by the size and power of the machine. This makes it extremely difficult for the designer to choose a suitable coefficient for the thermal analysis during the design stage of an electric motor. A methodology to obtain the end-windings convection heat-transfer coefficients for fractional-slot concentrated winding permanent-magnet synchronous motors is proposed in this article. Machine designs with both internal and external rotors will be considered. The experimental tests required for the model characterization are described in detail. In this article, general expressions of the convection heat-transfer coefficients between the end-windings and the housing end-caps are proposed for both internal and external rotor designs. Differences observed with the results reported in the literature are also discussed.