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

Strontium ferrite based permanent magnets 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 permanent magnets can efficiently replace an induction motor in low power applications, and why a round stator is a clear winner against a U-core permanent magnet motor