Iron losses in salient permanent magnet machines at field-weakening operation

Permanent magnet machines for electric vehicles are often designed with a magnetic saliency to improve the torque generation as a result of the reluctance torque at field-weakening operation. The armature reaction is pronounced in such operation, leading to extensive magnetic field harmonics in the teeth and consequently iron losses. This paper analyses the iron losses in two designed machine topologies, inset and interior permanent magnet rotor structures, by measurements and finite element method computations. The measurements and calculations are performed on three prototypes - one with an inset design and 'two with an equal interior design, but different laminated stator core sheet thickness of 0.35 and 0.20 mm, respectively. The three machines have the same stator designs and water-cooled housings.