Analysis and Compensation of Eccentric Unbalanced Magnetic Pulling Force in Bearingless Permanent Magnet Slice Motors Based on Magnetic Field Modulation Theory
Wang Suo, Wang Yu
College of Automation Engineering Nanjing University of Aeronautics & Astronautics Nanjing 210016 China
Abstract：Unbalanced magnetic pulling force significantly impacts the suspension performance of bearingless slice motors. Previous studies have overlooked the influence of stator slotting on an unbalanced magnetic pulling force, resulting in low model accuracy and average compensation effect. In addition, the existing models for analyzing the eccentric unbalanced magnetic pulling force of permanent magnet motors are unsuitable for bearingless permanent slice film motors that require high model accuracy. The existing models for bearingless permanent slice film motors do not consider the influence of stator slots, and the model accuracy is not high enough. Therefore, it is necessary to establish a high-precision analytical model that takes into account the influence of slotting to accurately analyze the unbalanced magnetic pulling force. The radial displacement of the rotor of a bearingless permanent magnet slice film motor during suspension is not zero. The geometric center of the rotor fails to be concentric with the geometric center of the stator, resulting in eccentricity. Such eccentricity distorts the originally sinusoidal air gap magnetic field and produces harmonics, which become the main source of unbalanced magnetic pulling force in thin film motors. A small amount of unbalanced magnetic pulling force generated from machining errors and asymmetric sensor installation is neglected. Therefore, accurately analyzing the air gap magnetic field under eccentricity is the key to accurately analyzing the unbalanced magnetic pulling force of bearingless permanent magnet slice motors. Combined with one-dimensional and two-dimensional analytical methods, this paper proposes an eccentric air gap magnetic field analysis method for bearingless slice film motors based on magnetic field modulation theory, considering the influence of stator slotting. The air gap magnetic permeability ratio measures the effect of slotting on the eccentric magnetic field of the motor, and the eccentric unbalanced magnetic pulling force is analyzed. Then, based on the theory of magnetic field modulation, the underlying mechanism of unbalanced magnetic pulling force is reanalyzed. It is proven that the model constructed in this paper has high accuracy and simple calculation. Finally, compensation experiments verify that precise compensation of unbalanced magnetic pulling force can greatly improve the suspension performance of bearingless slice motors. The proposed unbalanced magnetic tension model has an error of about 0.5% in simulation, significantly improving the accuracy. When compensating for the unbalanced magnetic tension of a thin film motor, it can significantly improve the suspension performance of the motor and reduce displacement to 15 μm, suitable for heart pump thin film motors with extremely high suspension performance requirements.
王锁, 王宇. 基于磁场调制理论的无轴承永磁薄片电机偏心不平衡磁拉力分析及其补偿[J]. 电工技术学报, 2025, 40(6): 1746-1757.
Wang Suo, Wang Yu. Analysis and Compensation of Eccentric Unbalanced Magnetic Pulling Force in Bearingless Permanent Magnet Slice Motors Based on Magnetic Field Modulation Theory. Transactions of China Electrotechnical Society, 2025, 40(6): 1746-1757.
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