Research on Sensitivity of Slot-Pole Combination to Unbalanced Electromagnetic Force Introduced by Rotor Eccentricity

Rotor eccentricity, which is commonly introduced during manufacturing, is an inevitable obstacle in achieving better vibration, noise, and harshness (NVH) performance. Therefore, a proper slot-pole combination less sensitive to eccentricity must be found to limit its negative effect. This paper investigates the sensitivity of slot-pole combinations to unbalanced electromagnetic forces introduced by static and dynamic eccentricity in permanent magnet synchronous machines (PMSMs) based on 72-slot/8-pole and 36-slot/24-pole PMSMs. The results show little difference in the magnitudes of new components introduced by the static and dynamic eccentricity for the same machine. More importantly, the negative effects of rotor eccentricity in fractional-slot PMSMs are twice more than that in integer-slot PMSMs, which means unbalanced electromagnetic forces in the low-frequency range are more sensitive to rotor eccentricity in fractional-slot PMSMs. Besides, the effectiveness of paralleled windings in suppressing unbalanced electromagnetic forces is different in the integer-slot and fractional-slot PMSMs.