Evolution and optimization of a brushless doubly‐fed machine with an asymmetrical reluctance and magductance rotor

Abstract

The brushless doubly‐fed machine (BDFM) utilizes an asymmetric composite rotor featuring salient pole reluctance and magductance to effectively compensate for the phase shift in space, as well as enhance magnetic field modulation effects, and is therefore used as a modulator. This paper evaluates the modulation capability of the modulator from the perspective of the magnetic field conversion mechanism. The theoretical evolutions of the average magnetic field conversion factors and torque contributions of various airgap field harmonics are accomplished. Additionally, multi‐objective optimization is conducted for better performance, using stratified sensitivity analysis on typical 4/2 pole pair BDFMs featuring symmetrical and asymmetric composite rotors. As a result, further improved modulation of the air gap magnetic field is expected, the cross‐coupling efficiency of the rotor is improved, and a lower output torque ripple is also achieved compared to the conventional symmetrical counterpart. Theoretical investigation of the optimized BDFM, including its effectiveness in enhancing performance metrics such as coupling factor, airgap flux density, and phase shift mechanism, is verified through 2D finite element analysis. Furthermore, a proof‐of‐concept prototype for experimentation was manufactured, which achieved good agreement with the theoretical predictions.