Analytical Prediction of Torque Ripple in Surface-Mounted Permanent Magnet Motors Due to Manufacturing Variations

Abstract

In the production of Surface-Mounted Permanent Magnet machines, manufacturing tolerances also contribute to torque ripple. Additional harmonics of low electrical orders are created in the torque spectrum. Slight manufacturing variations develop asymmetry conditions in the rotor as well as in the stator. Finite element models can be used to analyze the magnitude of pulsating torque generated due to these asymmetries. However, due to its random nature, lack of periodicity and symmetry, it is time consuming to study the problem with numerical methods for its uneven geometry that does not allow reduced geometrical models. Moreover, the experimental verification of all possible variations would be very challenging as it would require part dimensioning, part sorting, a large quantity of motor builds and finally testing of all samples. Therefore, in this paper an analytical model is presented to study the effect of such imbalance on the torque ripple. The model shows agreement against finite element models and also with experimental results when predicting torque harmonics that come from asymmetries.

Design of A Novel Line Start Synchronous Motor Rotor

“…Of course, this has led to giving more attention to the rotor cage design in order to ensure that the permanent magnets that are closer to the air gap do not have an adverse impact on the motor start. The torque fluctuations due to the impact of the permanent magnets are another issue that should be taken into consideration [31,32].…”

A new analytical technique for analysis and detection of air-gap eccentricity fault in surface-mounted permanent-magnet machines

“…The effect of manufacturing variations on the torque ripple and unbalanced magnetic pulling (UMP) has been studied in Ortega and Xu using an analytical model.…”

“…The models presented in previous studies have not been focused on the eccentricity fault effects on the machine voltages or currents. However, the models can help designers to quickly understand the origin of cogging and ripple torque harmonics in any stage of design process, without proposing asymmetrical models and solving them through finite element method.…”

“…Although, the model is based on a complete subdomain model, the impact of tooth-tips, variation in stator geometry, and the effect of magnet pole shaping were not studied in Qian et al 21 An analytical model of the variations in the rotor as well as the stator geometry, such as magnet dimension and displacement, stator slot opening, and height of the slot opening, have been studied in Pina et al 22 It is based on a complete subdomain model including slot opening and glue gap regions, and the model is presented to study the effect of such imbalance on the cogging torque.The effect of manufacturing variations on the torque ripple and unbalanced magnetic pulling (UMP) has been studied in Ortega and Xu 23,24 using an analytical model. The models presented in previous studies [21][22][23][24] have not been focused on the eccentricity fault effects on the machine voltages or currents. However, the models can help designers to quickly understand the origin of cogging and ripple torque harmonics in any stage of design process, without proposing asymmetrical models and solving them through finite element method.…”

“…The effect of manufacturing variations on the torque ripple and unbalanced magnetic pulling (UMP) has been studied in Ortega and Xu 23,24 using an analytical model. The models presented in previous studies [21][22][23][24] have not been focused on the eccentricity fault effects on the machine voltages or currents. However, the models can help designers to quickly understand the origin of cogging and ripple torque harmonics in any stage of design process, without proposing asymmetrical models and solving them through finite element method.…”