Nowadays, the field-modulated permanent magnet (FMPM) machines have attracted significant attention in direct-drive applications. However, the rare-earth PMs have fluctuation price
and unstable supply. Thus, the rare earth reduction of FMPM machine is extensively regarded as a candidate for electric vehicles 1. It is investigated that the rotor consequent-pole PM
(R-CPM) machine exhibits higher torque capability than the stator CPM machine because of the fact that various rotor permeance harmonics are more involved in torque generation 2.
Based on the study, this paper designs and analyzes a new FMPM machine with one airgap, which adopts the half Halbach array PMs embedded in the rotor slot and possesses the merit of
high PM utilization ratio.
II.Topology and Operation Principle
As shown in Fig. 1, the proposed FMPM machine consists of rare earth PMs and windings, which are located in the rotor and stator respectively. Compared to the existing FMPM machine,
the key difference is that half Halbach array PMs are employed in rotor slot. The rotor teeth, which provide a mechanical support and better effect of heat dissipation for PMs, build the
routes for the fields of PM and armature winding.
Fig. 2(a) presents the no-load phase back-EMFs of the existing and proposed FMPM machines under the same speed. It can be observed that the maximum back-EMF obtained by the
proposed HEFM machine is similar to the existing machine that excited by both rare earth PMs and ferrite PMs. Fig. 2(b) shows that the torque densities with the same rated armature
current of 5Arms. It is found that the torque density of the proposed machine is similar to the superposition of torque produced by the machines with rare earth PMs and ferrite PMs, while
the PM volume is only 66% of the existing one. It proves the effectiveness of the improved rotor structure.
1 C. Gong and F. Deng. Design and optimization of a high-torque-density low-torque-ripple vernier machine using ferrite magnets for direct-drive applications. IEEE Transactions on
Industrial Electronics, vol. 69, no. 6, pp. 5421-5431, June 2022.
2 Y. Li, H. Yang and H. Lin. Comparative study of torque production mechanisms in stator and rotor consequent-pole permanent magnet machines. IEEE Transactions on Transportation
Electrification, vol. 7, no. 4, pp. 2694-2704, Dec. 2021.