Rotor Yoke Effect on Core Losses of a Non-Overlap Wound-Rotor Synchronous Machine

The focus of the paper is on the reduction of core losses of large wound-rotor synchronous machines with non-overlap stator windings. The wound-rotor synchronous machine, being one of the alternatives to the permanent magnet synchronous machine, has the important advantage that the rotor field flux can be varied. The use of non-overlap stator windings is growing due to the associated improved torque density and simpler manufacturing, but at the expense of a higher harmonic content in the magnetomotive force distribution. The latter causes the core losses in wound-rotor synchronous machines to increase. This paper shows that the rotor yoke design has an important effect on these losses. Rotor yoke design strategies are applied in the paper to limit the amount of harmonic flux setup in the rotor core. Flux barriers in the rotor yoke are deemed to have the overall best effect on the machine performance by reducing the rotor core losses while not increasing torque ripple and maintaining output power.