Abstract
Two novel structures of permanent magnet (PM) machine, namely a hybrid excitation flux modulation machine (HEFMM) and a variable flux memory machine (VFMM), which have excellent field-weakening capability, are presented in this paper. The HEFMM incorporates the advantages of parallel hybrid excitation structure and flux modulation structure, so as to increase the torque density as well as increase the constant-power speed range. Inspired by the HEFMM, aiming to further improve the efficiency of machine, the VFMM with aluminum-nickel-cobalt (AlNiCo) PMs in the inner stator which can be magnetized by the current pulse of the direct current (DC) windings is developed. With double-stator structure, flux modulation effect in both machines can be employed to realize the hybrid excitation and regulate the air-gap flux density readily. The operation principle is illustrated and the static and steady performances of the machines are analyzed and compared with time stepping finite element analysis, which validates the effectiveness of the proposed designs.
Highlights
Permanent magnet (PM) machines with high efficiency and high torque density have found extensive applications in various fields
Wide speed range constant-power operation is usually required in a variety of industrial applications such as in electric vehicles and wind power generation systems
The field-weakening performance of PM machines is usually limited by the magnet flux-linkage and the saliency ratio
Summary
Permanent magnet (PM) machines with high efficiency and high torque density have found extensive applications in various fields. The field-weakening performance of PM machines is usually limited by the magnet flux-linkage and the saliency ratio. Li and Lipo [3] proposed a new type of hybrid excited doubly salient PM machine capable of field weakening, which incorporates both PMs and wound field windings in the stator. For this design, the PMs are the major source of the air-gap flux. The DC current enhances the air-gap flux for high torque density. Μ0 is the vacuum permeability and μr is the relative permeability of PMs. According to Equations (1) and (2), the inner air gap flux density is shown as:. For the flux modulation machine, the inner rotor PM poles are replaced by the stator windings. The stator flux linkage is same as the expression Equation (7) due to the flux modulation effect of the outer rotor PMs
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