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An eccentric position diagnosis method of static eccentricity (SE) fault of external rotor permanent magnet synchronous motor (ER‐PMSM) is presented. Firstly, an analytical model of no‐load radial magnetic field of ER‐PMSM is established. Analytical models of no‐load Back‐EMF of both unit motors and the whole motor are carried out and are verified by finite element method (FEM) and experimental measurements. Then, the influences of SE ratio, SE circumferential angle, winding distribution mode and number of parallel branches on no‐load radial magnetic field and no‐load Back‐EMF are analyzed based on these analytical models. The results show that SE does not affect the frequency characteristics of no‐load radial magnetic field, but changes space order characteristics. On one hand, for ER‐PMSM, of which the number of unit motors is equal to 1, SE causes no‐load Back‐EMF distortion. On the other hand, for ER‐PMSM, of which the number of unit motors is greater than 1, SE does not affect no‐load Back‐EMF of the whole motor, but it still leads to no‐load Back‐EMF distortion of unit motors. Therefore, based on total harmonic distortion (THD) of no‐load Back‐EMF of unit motor, a projection method of intersection lines for SE fault diagnosis of ER‐PMSM is proposed finally. [ABSTRACT FROM AUTHOR]

The no‐load radial magnetic field and no‐load back electromotive force (EMF) of external rotor permanent magnet brushless DC motor (PMBLDCM) are calculated by applying the correction coefficient of magnetic conductance here, taking into account the stator slotting and static eccentricity effects. An external rotor PMBLDCM with 51‐slot/46‐pole, used as in‐wheel motor, is taken as an example, the analytical calculation results of the no‐load back EMF are validated by the finite‐element method and experiment. The influences of static eccentricity ratio on the no‐load radial magnetic field and no‐load back EMF are investigated based on the analytical model. The investigation shows that static eccentricity does not change the harmonic contents of no‐load radial magnetic field, so it does not change the harmonic contents of three‐phase no‐load back EMFs. However, static eccentricity changes the space order of no‐load radial magnetic field, resulting in the different total harmonic distortions of three‐phase no‐load back EMFs; in other words, the asymmetric distortions of three‐phase no‐load back EMFs are generated. The asymmetric distortions of three‐phase no‐load back EMFs are intensified with the increase in static eccentricity ratio. [ABSTRACT FROM AUTHOR]

Here, analytical expressions of the unbalanced magnetic force (UMF）of the stator and the rotor under static eccentricity (SE) are deduced by using complex relative magnetic conductivity method and Maxwell stress tensor method. The frequency characteristics of the UMF are obtained. Further the influence of different eccentricity ratio on the UMF is researched. Then, an external rotor permanent magnet brushless direct current motor (PMBLDCM) with 46 poles and 51 slots used as an in‐wheel motor is taken as an example to verify the frequency characteristics by finite element analysis (FEA). The research shows that the frequency characteristics of the UMF of the stator s related to electric frequency. The frequency characteristics of the UMF of the rotor are related to the power source frequency and the rotation frequency of the wheel. It does not introduce new frequency components when the motor SE occurs. As the SE ratio increases, the amplitude of the UMF increases. The UMF without eccentricity exists in all directions with the change of the time. However, as the eccentricity ratio increases, the direction of the UMF is closer to the eccentric direction. [ABSTRACT FROM AUTHOR]