volume | PIER Journals

Abstract

In conventional permanent magnet-assisted synchronous reluctance motors (PMaSynRMs), the peak current angles of permanent magnet (PM) and reluctance torques are theoretically separated by 45 electrical degrees, which prevents full superposition of the two torque components and limits torque density improvement. This paper proposes a novel asymmetric rotor topology based on the principle of magnetic flux linkage phase-shifting (MFS). The proposed topology reconfigures the rotor magnetic circuit by shifting a bar-shaped PM to the junction center between two adjacent reluctance segments and removing the PMs on one side of the U-shaped flux barriers (so that magnets are only placed on one side of the pole). This forces a controllable shift of the effective electromagnetic d-axis. A unified torque mathematical model incorporating the current angle β and the magnetic axis shift angle γ is established, revealing the regulation mechanism of flux linkage phase shift on the phase characteristics of torque components. Taking a 4 kW, 8-pole ferrite PMaSynRM as the research object, a multi-objective optimization is carried out using the Kriging surrogate model and the Non-dominated Sorting Genetic Algorithm III (NSGA-III). Finite element simulation results show that the effective d-axis of the optimized motor shifts by 45 electrical degrees, achieving nearly full peak alignment of PM torque and reluctance torque at the same current angle. With a 7.8% reduction in ferrite PM usage, the utilized PM torque increases from 13.88 N·m to 16.82 N·m (an increase of 21.2%); the total output torque rises from 38.67 N·m to 40.32 N·m (an increase of 4.27%); torque ripple decreases from 9.15% to 6.09%; and efficiency remains stable. Furthermore, under a direct-axis demagnetization condition with twice the rated current, the proposed asymmetric topology exhibits no local demagnetization, demonstrating better demagnetization resistance than the conventional symmetric motor. This study provides an effective approach for high torque density design of low-cost ferrite electric drive systems.

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Dr. Chaozhi Huang

Mr. Fangrong Wang

Mr. Wen Kuang

Mr. Long Chen