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.
Highlights
Permanent magnet (PM) machines with rare-earth materials, e.g., NdFeB, have been widely adopted in various applications, including electric and hybrid electric vehicles, owing to their high torque density and efficiency [1,2,3]
The 12/10-stator/rotor-pole partitioned stator wound field switched flux (PS-WF switched flux (WFSF)) machine without ferrites is shown in Fig. 1a, and it consists of an outer stator wound by armature windings, an inner stator wound by DC windings, and a sandwiched rotor composed of several iron pieces
Since the on-load inner stator tooth saturation in the PS-WFSF machine without ferrites is stronger than the open-circuit one owing to armature reaction, the average electromagnetic torque can be more effectively increased by 3.77% from 1.47 N·m to 1.53 N·m, when both the DC winding copper loss and the AC windings copper loss are 30 W and the machines operate in the brushless AC (BLAC) mode under id=0, because of negligible reluctance torque [28]
Summary
Permanent magnet (PM) machines with rare-earth materials, e.g., NdFeB, have been widely adopted in various applications, including electric and hybrid electric vehicles, owing to their high torque density and efficiency [1,2,3]. Based on the magnetic gearing effect in stator-excitation machines [23,24,25,26,27], a partitioned stator WFSF (PS-WFSF) machine with separated DC and AC windings in two stators was proposed and analyzed in Zhongze Wu et al.: Enhancement of Torque Density in Wound Field Switched Flux Machines with. To further increase the torque density and overload capability of the 12/10-stator/rotor-pole PS-WFSF machine shown in Fig. 1a but not introduce any rare-earth PM, based on the contents reported in Ref.
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