High Power Density Permanent Magnet Machines With Multiwinding Structure for Enhancing Harmonic Torques

Permanent magnet (PM) machines have been widely adopted due to their advantages of high power density and efficiency. In this article, the further improvement of the power density for the PM machines without worsening the power factor is studied, where the harmonics are utilized efficiently for torque generation. The magnetic field modulation in the PM machines is introduced first. Then, the torque generation mechanism is investigated considering the modulated armature and permanent magnetic fields. The quantitative analysis of harmonics in the air-gap magnetic field contributing to the electromagnetic torque is conducted and multiwinding scheme is adopted for enhancing the harmonic torques. The electromagnetic performance of the proposed PM machine is analyzed and compared with that of the PM vernier machine (PMVM). Finally, a prototype machine is manufactured and tested to verify the theoretical analysis. It is shown that the proposed PM machine has the merits of high torque density, high power factor, and high PM utilization.