Pole-changing Field Modulation Permanent Magnet Motor based on Magnetomotive Force Offset

This paper proposes a new pole-changing (PC) design method for rotor-permanent-magnet (RPM) motors based on magnetomotive force (MMF) offset (MMFO), which is realized by offsetting the magnetic pole positions of permanent magnet (PM) MMF to introduce even-order harmonics. The newly introduced PM MMF harmonics and the original PM MMF harmonics can both interact with the air-gap permeance harmonics to generate PM air-gap flux density harmonics with different slot phasor diagrams, making it possible to realize PC. The design principle of MMFO is specifically investigated, based on which a PC-MMFO motor using modular MMFO structure is further proposed. The operating principle of the PC-MMFO motor is then discussed. By finite element analysis, the motor performance is analyzed and verified by experiments. The results show that the proposed motor possesses a high torque and a wide high-efficiency speed regulation range.