Influence of end winding configuration on the performance of slotless homopolar hybrid active magnetic bearings

Homopolar hybrid active magnetic bearings (HH-AMB) generate very low power losses, that can be further reduced using slotless toplogies. Indeed, the slot openings create local fluctuations of the magnetic flux density, which are at the origin of iron losses in the rotor. Such slotless HH-AMB have already been proposed, but no particular considerations have been given to the end winding (EW) configuration, although slotless topologies offer more flexibility than slotted topologies on this aspect. In this paper, four different EW configurations are compared, based on performance criteria which are evaluated and optimized by means of an analytical electromagnetic model. The results show that the winding whose EW can be inset in the airgap and can overlap provides the best performance, with a reduced volume of permanent magnet.