New interior PM rotor design with high flux-weakening capability

Abstract

Interior permanent magnet (IPM) synchronous machines attract attentions, due to their excellent torque/power density and high efficiency. Comparing to surface PM (IPM) machines, interior PM machines has higher flux weakening capability at high speed, which is suitable for vehicles. It is of interest to keep Constant Power Speed Range (CPSR) condition in wide speed range. Magnet segmentation proposed by several authors to increase IPM flux weakening capability. The basic idea is to provide proper paths for the stator d-axis flux (Ld*Id) (or increasing d-axis inductance Ld) by thin iron-bridge between magnet segmentations. This paper proposes a new IPM rotor design which improves flux weakening while keeping rated torque at low speed. First, the sensitivity of negative d-axis current id in decreasing air-gap flux is evaluated by FEA. Then optimum positioning and sizes of new magnet-segmentations, air-bridges and iron-bridges are presented. The optimization result in removing the iron-bridge at the outer rotor circumference and adding equivalent iron-bridge width in between magnet segmentations. This has same mechanical rotor integrity strength while providing flux weakening without decreasing rated torque. Finally, the torque-speed characteristic is obtained and compared with similar method.