A High Torque Density Ferrite STPM Motor Using Flux-Leakage Utilized Rotor

This article presents a particular flux-leakage that utilized a permanent magnet (FLUPM) rotor for ferrite spoke-type permanent magnet (STPM) motors to improve torque density. The key is to build a toroidal magnetic field (TMF) between the rotor yoke and N-pole, and TMF is only formed by the S-pole flux-leakage. In addition, to enhance the TMF, the S-pole usage is increased to generate more flux-leakage. Moreover, the magnetic barrier is reasonably designed to prevent flux flow to the shaft. Thus, a strong TMF utilizing S-pole flux-leakage is established. The TMF with strong flux shielding effect reduces the N-pole flux leakage, forcing more flux flow to the air gap. As a result, the flux-concentrated capacity of the rotor is significantly improved, thus enhancing the output torque. Through theoretical analysis, finite element simulation, and prototype test, it is confirmed that the FLUPM motor has a higher output capacity than the STPM motor already in mass production. Meanwhile, the torque ripple and cogging torque performance do not become worse. Furthermore, the FLUPM motor can achieve the IE5 energy-efficiency class with a lower material cost.