A Method to Improve Torque Density and Reduce Magnetization Current in a Variable-Flux Flux-Intensifying Interior Permanent Magnet Machine

This paper mainly proposes a method to improve torque density and reduce magnetization current of a variable- flux flux-intensifying interior permanent magnet machine (VFI-IPM) which utilizes low coercive-force magnet material AlNiCo. Since the d-axis inductance is higher than q-axis inductance in the VFI-IPM and the saliency ratio is not that high as conventional IPM machine, the reluctance torque of the VFI-IPM is low which is not favorable for high torque density and wide constant power region. What's more, the remnant magnetism of AlNiCo is always lower than rare-earth magnets, leading to a lower torque output. So it's necessary to take measures to obtain high torque density. On the other hand, the magnetization current of VFI-IPM is a key parameter for inverter rating which affects the cost the machine directly. Therefore, it's also needed to investigate methods to reduce the magnetization current. A method is proposed to improve the torque density and reduce the magnetization current based on the original topology of the VFI-IPM which includes the process for rotor molding.