Performance Improvement in Flux-Switching PM Machines Using Flux Diverters

Several schemes for mechanical (as against electrical) flux weakening in permanent-magnet (PM) machines have been proposed in recent literature. Although the detailed arrangements differ depending upon whether the magnets are mounted on the rotor or the stator, the principle remains broadly the same. A movable piece of magnetic steel is used to “short” or divert the magnet flux such that the amount of flux crossing the airgap can be varied between a maximum and a minimum level. While previous work on mechanical flux weakening in flux-switching PM machines has emphasized performance improvement achieved mainly through enhanced operating speed range, this paper, based on both analytical and experimental results, demonstrates performance improvement in three other areas, namely, reduction in electromotive force at maximum speed, reduction in open-circuit loss, and enhancement in efficiency under light load.