A Novel Split-Tooth Bidirectional Field Modulation Permanent Magnet Motor for Low-Speed High-Torque Direct-Drive Systems

This paper proposes a split-tooth bidirectional field modulation permanent magnet (PM) motor (ST-BFMPMM) for low-speed, high-torque, direct-drive applications. Featuring a compact single-stator, single-rotor configuration with a tangentially magnetized split-tooth stator and a consequent-pole rotor incorporating radially magnetized PMs, the proposed topology realizes bidirectional field modulation to enhance the utilization of torque-producing harmonics while reducing the total PM requirement. Three pole–slot configurations (12s14p, 12s17p, and 12s19p) are optimized using finite element analysis (FEA), and the 12s19p design exhibits the best overall performance. Compared with the conventional 12s17p benchmark, its rated torque increases by 51.93%, PM consumption decreases by 39.4%, and torque ripple is reduced to 2.57%. It also achieves a 55.9% higher fundamental back-EMF and 2.51 times the torque output per unit PM area, while maintaining nearly the same calculated rated efficiency (96.88% versus 96.87%). Although the higher fundamental back-EMF causes the proposed motor to enter voltage-limited operation at a lower speed, thereby limiting its high-speed torque capability, the proposed motor provides high torque output and improved PM utilization in the targeted low-speed range, making it a promising candidate for gearless direct-drive wind turbines and heavy agricultural machinery.