Enhancement of torque density in wound field switched flux machines with partitioned stators using assisted ferrites

Abstract

In this paper, ferrites are applied in a partitioned stator wound field switched flux (PS-WFSF) machine to increase the air-gap flux density, and hence, the average electromagnetic torque and overload capability. Introducing short-circuited ferrites in the inner stator in the PS-WFSF machine can increase the open-circuit phase fundamental back-EMF and average electromagnetic torque at a 60 W copper loss by 2.33% and 3.77%, respectively. Moreover, the proposed PS-WFSF machine with ferrites can exhibit a better overload capability than conventional PS-WFSF machines without ferrites, e.g., a 7.36% torque increment can be achieved when the copper loss is 120 W. The torque increment mechanism is analyzed and verified using finite element (FE) analysis. Moreover, the demagnetization of the ferrites in the proposed machine under rated on-load and overload conditions is investigated. Both prototypes of the proposed PS-WFSF machine with ferrites and a conventional one without ferrite are built and tested to validate the analytical and FE analyses.