Torque Performance Improvement via Amplitude-Phase Collaborative Modulation From the Perspective of Excitation-Source Offset in Asymmetric Salient-Pole PMSMs

Salient-pole permanent magnet synchronous machines (SP-PMSMs) are characterized by high torque density owing to the simultaneous production of PM torque and reluctance torque. However, in conventional symmetric pole structures, the peak values of these two torque components cannot coincide at the same current phase angle, resulting in their underutilization. This paper establishes a multi-working-harmonic model for both the initial and the excitation source offset SP-PMSMs by the magnetic field modulation analysis method, which includes the excitation source, the relative permeance of the modulators, and the airgap flux density, the contribution of the amplitude and phase of each working harmonic to torque enhancement is derived, i.e., amplitude-phase collaborative modulation. Furthermore, from the perspective of the fundamental wave, the PM torque and reluctance torque are modeled, and the difference in current phase angles corresponding to their respective maximum values is determined, which subsequently guides the topological design of the asymmetrical SP-PMSM. Finite element analysis (FEA) and experimental tests demonstrate that the proposed method effectively improves torque performance: the average torque is increased by 20.74% without additional PM material, while torque ripple is reduced by 6.82%. The proposed method can effectively improve the machine torque quality and provide direction for the design of asymmetrical SP-PMSMs.