Demagnetization Assessment of Fractional-Slot and Distributed Wound 6-Phase Permanent Magnet Machines

A 6-phase fractional-slot-per-pole-per-phase interior permanent magnet (IPM) machine having a novel topology of 18-slot, 8-pole and a 6-phase, 48-slot, 8-pole IPM with distributed windings, both designed for a segment-A electric vehicle, are assessed for the risk of partial irreversible demagnetization under various fault conditions. This paper describes a more accurate approach of demagnetization assessment based on 2-D transient finite-element analysis. It is shown that due to the presence of low-order space harmonics in the fractional-slot IPM machine, the demagnetization risks across all pole pairs are different. Compared with the distributed wound machine, the fraction-slot machine is less vulnerable to demagnetization due to relatively high winding inductance, although its demagnetized regions are not uniform in each pole. It is also shown that although the demagnetizing current of one 3-phase short-circuit (SC) is greater than that of 6-phase SC, the resultant demagnetization risk is lower than that of 6-phase SC in the fractional-slotmachine.