Design and comparison of interior permanent magnet synchronous motors with non-uniform airgap and conventional rotor for electric vehicle applications

In recent years, electric mobility is becoming a growing reality because of the increase of the oil demand and cost as well as the environmental effect of the conventional internal combustion engines. Since about a decade, in the USA, a public-private cooperative research initiative, called FreedomCAR (US Drive by mid 2012) has been working for developing high efficiency and cost competitive technologies for the electrification of private transport. This research presents the design and the comparison of two high performance, radial magnetisation, interior permanent magnets and synchronous motors, according to the FreedomCAR targets, equipped with different rotor shape geometries. The first is characterised by a non-uniform airgap, whereas the second presents a conventional rotor shape. Both the machines are equipped with the same stator and a fractional slot concentrated winding. This paper highlights the benefits for using a non-uniform airgap rotor design, especially concerning the efficiency, that represents the most difficult target to be satisfied.