Demagnetization Performance Characteristics of Flux Switching Permanent Magnet Machines

This paper investigates the static demagnetization behavior of flux-switching permanent magnet (FSPM) machines during normal operating conditions. A combination of spatial harmonic analysis, magnetic equivalent circuits, and finite element (FE) analysis has been used to study the flux paths associated with the stator windings and their interaction with the permanent magnets (PMs) located on the stator. The MMF contributed by the stator currents under a variety of operating conditions combines constructively with the magnet MMF to augment the flux density in the PMs. This behavior has important ramifications for avoiding irreversible demagnetization caused by stator current MMFs impressed on the PMs. This analysis shows that, in contrast to many types of PM synchronous machines, FSPM machines do not produce demagnetizing MMFs during normal operation that threaten to demagnetize the magnets. This opens opportunities to consider the use of less expensive, lower energy-product materials for the PMs, including ferrite magnets or rare-earth materials with a lower concentration of dysprosium.