Reduction of Local Tangential Force of Fractional-Slot Concentrated Winding Permanent Magnet Synchronous Machines with Piecewise Stagger Trapezoidal Poles
Li Zexing1, Xia Jiakuan1, Liu Tiefa2, Guo Zhiyan1, Lu Bingna1
1. School of Electrical Engineering Shenyang University of Technology Shenyang 110870 China; 2. Shenyang Institute of Automation Chinese Academy of Science Shenyang 110169 China
Abstract:The permanent-magnet synchronous machines (PMSMs) are the most attractive candidates to use as power sources for underwater vehicles due to their inherent high efficiency and high power density. However, as an essential performance for underwater vehicles, concealment is vulnerable to low-frequency vibration and noise caused by PMSMs. The local tangential electromagnetic force is a vital excitation source. For the fractional slot permanent magnet motor, the local tangential electromagnetic force will cause radial vibration of the stator yoke through the lever effect of stator teeth. Its contribution to vibration can be comparable with that of radial electromagnetic force. Therefore, analyzing and weakening the local tangential electromagnetic force is necessary. This paper proposes a weakening method of piecewise stagger trapezoidal poles. The magnetic poles are equally divided into two sections in the axial direction, and the two-section magnetic pole is symmetrically distributed along the axial direction. On each rotor surface, two adjacent magnetic poles in the circumferential direction have opposite polarities, and the axial arrangement is reversed. The center of each magnetic pole of the proposed motor is the same as that of the common motor. The shape of the magnetic pole is similar to the trapezoid. The beveled edge of each magnetic pole is continuously skewed, connecting the short and long sides. Based on the finite element model, the tangential force, tangential moment and main electromagnetic parameters of the common motor without an optimized structure and the proposed motor with the optimized structure are calculated and compared. The tangential force density curves of the two motors are calculated. Compared with the common motor, the peak-to-peak value of the tangential force density is reduced by 20 % for the proposed motor. The tangential concentrated force curves and their FFT results of the two motors are calculated. Compared with the common motor, the peak-to-peak value of the tangential concentrated force decreases from 475 N to 370 N, and the amplitudes of the 2nd and 4th harmonics are reduced by 23 % and 42 % for the proposed motor. The tangential moment curves and their FFT results of the two motors are also calculated. Compared with the common motor, the peak-to-peak value of the tangential moment decreases from 595 mN·m to 415 mN·m, and the amplitudes of the 2nd, 4th, and 6th harmonics are reduced by 25 %, 43 %, and 36 % for the proposed motor. The electromagnetic torques of the two motors are simulated and compared on load. The average torques of the two motors are 4.21 N·m and 4.26 N·m, respectively, and the torque density of the proposed motor is unchanged. The vibration acceleration spectra of the two motors at rated speeds are simulated and compared. Compared with the common motor, the reduced proportions of the acceleration amplitude at 2f, 4f, and 6f reach 50.5 %, 51.5 %, and 53.5 % for the proposed motor. Two prototypes are manufactured, and the vibration experiments are carried out. The trends of the simulated and measured results are consistent. Compared with the common motor, the amplitudes of the vibration acceleration at 2f, 4f, and 6f are reduced significantly for the proposed motor. The relationship between the torque and current of the two motors is measured. When the phase current reaches the rated current, the average torques of the common and proposed motors are 4.22 N·m and 4.25 N·m, respectively. Therefore, the optimized structure of the piecewise stagger trapezoidal poles can effectively reduce the pole-frequency vibration while ensuring the torque density.
李泽星, 夏加宽, 刘铁法, 郭志研, 鲁冰娜. 基于分段交错梯形磁极的分数槽集中绕组永磁电机局部切向力的削弱[J]. 电工技术学报, 2023, 38(6): 1447-1459.
Li Zexing, Xia Jiakuan, Liu Tiefa, Guo Zhiyan, Lu Bingna. Reduction of Local Tangential Force of Fractional-Slot Concentrated Winding Permanent Magnet Synchronous Machines with Piecewise Stagger Trapezoidal Poles. Transactions of China Electrotechnical Society, 2023, 38(6): 1447-1459.
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