Investigation of Torque Improvement Mechanism in Emerging Switched Flux PM Machines

This article aims to investigate and reveal the torque enhancement mechanism in several emerging switched flux permanent magnet (SFPM) machines using a unified torque equation with an improved winding factor function. Based on a hybrid finite-element (FE)–analytical method, the torque contributions of the major air-gap field harmonics in the conventional, C-core and E-core, and consequent-pole (CP) SFPM machines are identified and quantified by taking a conventional 12-stator-slot/13-rotor-tooth (12s13r) SFPM machine as a benchmark, which shows that the dominant torque proportions are contributed by the low-order field harmonics due to the amplification effect of the gear ratio. Besides, a low-order field harmonic impeding effect is observed in the conventional and C-core SFPM structures, resulting in a compromised torque capability. Whereas since the auxiliary teeth and stator iron bridge designs provide relatively lower magnetic reluctances for low-order harmonics, the E-core and CP structures can produce improved low-order harmonics and higher torques than the conventional one. Finally, some experiments on a CP-SFPM machine are conducted to validate the theoretical and FE analyses.