Performance Analysis of Permanent Magnet Machines with Harmonic-Injected Magnets of Varying Segmentation

Manipulating the shape of permanent magnets (PMs) to control the air-gap magnetic field waveform of electric machines is an effective method for enhancing motor output performance. Current methods for third-harmonic injection in PMs are primarily based on theoretical derivations from radially magnetized configurations. However, in practical manufacturing, due to cost and processing constraints, PMs are often fabricated using parallel magnetization techniques. For small-sized, low-pole-pair applications, where the angular span of each PM is relatively large, the theoretical formulas derived for radially magnetized configurations become less applicable. This paper proposes a segmented PM approach to improve the applicability of radially magnetized theories by segmenting the PMs after harmonic injection. First, the paper derives and validates shape functions for PMs with different segmentation numbers. Subsequently, a comparative analysis of the air-gap magnetic field waveform and back-EMF waveform is conducted. The average output torque and torque ripple of the machine are then investigated. Finally, the demagnetization coefficients of PMs with different shapes are compared. Results demonstrate that segmenting the PMs effectively enhances the output performance of the harmonic injection method in low-pole-pair applications.