Performance comparison of U-Core and round-stator single-phase permanent-magnet motors for pump applications

Strontium-ferrite-based permanent magnets (PMs) are attractive for applications in electric machines due to several reasons. Their price is some two orders of magnitude less than the price of rare-earth magnets. They are chemically inert, which makes them suitable for applications in aggressive environments. Strontium-ferrite magnets have high specific electric resistance, so they do not experience thermal problems due to eddy-current losses. On the other hand, their low residual flux density imposes the need for special machine construction when high air-gap flux density is needed. It is shown in this paper how a synchronous motor with strontium-ferrite PMs can efficiently replace an induction motor in low-power applications, and why a round stator is a clear winner against a U-core PM motor.