Field-weakening Capability of Interior Permanent Magnet Machines with Salient Pole Shoe Rotors

Brushless permanent magnet (BLPM) machines, with inherent advantages of high power density and high efficiency, have been widely employed to achieve traction characteristics for traction application. Generally, traction characteristics require high torque at low speed and wide field-weakening region keeping constant power. However, both conventional interior permanent magnet (IPM) and surface-mounted permanent magnet (SPM) machines suffer from high speed issues in the field-weakening region. A different BLPM machine topology, the pole shoe topology, is proposed in this paper. Although the pole shoe machine is common in industrial variable speed drives employing constant torque regimes, it has not been previously considered for machines designed for a wide field-weakening region. For analysis and comparison, a conventional IPM machine, which is employed as the Nissan Leaf vehicle traction machine, is studied as a reference benchmark machine. Experimental results from this machine are used to validate the analysis presented in the paper. The design results show that the proposed pole shoe machine achieves better field-weakening performance, compared with the conventional IPM and SPM machine topologies.