Performance analysis of rare-earth and rare-earth free external rotor motors under eccentricity faults

Abstract

This paper presents the performance comparisons between rare-earth and rare-earth free external rotor permanent magnet assisted synchronous reluctance motors (PMa-SynRMs) under static eccentricity (SE), dynamic eccentricity (DE), and mixed eccentricity (ME) conditions. Recently, external rotor motors are proposed as high power density motors for traction applications in electric vehicles and more electric aircraft. However, these in-wheel external rotor motors are usually under continuous stress of rotational forces due to the tire-road friction which can result in eccentricity faults due to stator and rotor misalignment. Therefore, it is critical to assess the external rotor motors performance under eccentricity faults in traction motors. In this study, various failure modes due to eccentricity faults such as SE, DE, and ME conditions are analyzed on optimal 3.8kW rare-earth based and 3.7kW rare-earth free external rotor PMa-SynRMs. Effects of these eccentricity conditions are translated to performance loss in terms of increased torque ripple and unbalanced magnetic pull (UMP) in the electric motor designs. Also, 3rd harmonics of back-electromotive force (back-EMF) have been analyzed for both motors in all eccentricity conditions to compare their performance in fault detection. Experimental setup is developed to test the motors under load conditions and finite element simulation results are presented to validate the proposed theory.