Impact of Stator Core Magnetic Asymmetry on the Properties of a High Specific Power PMSM

Permanent Magnet Synchronous Machines (PMSMs) are commonly employed in applications demanding a high specific power. To achieve high specific power values, a high pole pair number PMSM with very thin yokes can be built. Such a design leads to a high operating frequency. At high operating frequencies, AC losses can more than double the DC losses if solid hairpin technology or traditional bunches of nontransposed round enameled wires are used in the stator windings of machines with a considerable power. Against this negative effect, the emerging Litz wire coil technology with prefabricated coils can be used. In this study, firstly, alternative stator slot geometries required when using prefabricated Litz wire coils are evaluated. A symmetric semi-closed slot is not suitable for inserting such prefabricated Litz wire coils into the stator slots. Instead, an asymmetric semi-closed slot can be used, and it may even offer a better performance than the symmetric open slot. After showing that the asymmetric semi-closed slot provides a better performance, it is investigated how this asymmetric stator slot geometry can be used beneficially. The findings were first studied with finite element analysis (FEA) and then experimentally verified on a high-specific-power machine.