Electric drive for an in-wheel fractional-slot axial flux machine

This paper describes the electric drive for an in wheel fractional slot axial flux machine designed for achieving a wide flux weakening operating region.By using a slotted stator with fractiona slot windings and additional cores enclosing end windings the axial flux machine reaches a wide constant power speed range. The machine is designed for increasing flux weakening capability while obtaining low harmonic back electromotive force and low cogging torque.A 10 N m axial flux machine exhibiting 3 to 1 flux weakening speed range has been built.A flux weakening controller able to maximize the output torque in the flux weakening region is designed and implemented.The goodness of both design and control algorithm is proved by experimental tests.However such a fractional slot machine has not only advantages.Rotor losses are very high and they have to be properly considered during the design process.