New magnet shape for reducing torque ripple in an outer-rotor permanent-magnet machine

Torque ripple is a major problem for permanent-magnet (PM) machines. It is examined by focusing on the magnetic circuit of the PM machine. Because there is a relationship between the torque ripple and the magnetic energy that is stored in the magnetic eld along the air gap of the PM machine, a variation in the magnetic energy was revealed initially. A new magnet geometry is obtained by forming ledges and notches in the permanent magnets to modify the variation of the magnetic energy and the uctuation in torque. Thus, a new PM design is proposed in this study to minimize the torque ripple of an outer-rotor surface-mounted PM machine. An improvement of 44.6% in the torque ripple is achieved thanks to the new magnet design. In addition, improvements are made in the average torque and the total harmonic distortion of the back electromotive force.

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[1] Lee SH, Han KK, Ahn HJ, Kang GH, Son YD, Kim GT. A study on reduction of vibration based on decreased cogging torque for interior type permanent magnet motor. In: 2008 IEEE Industry Applications Society Annual Meeting; 5{9 October 2008; Alberta, Canada. New York, NY, USA: IEEE. pp. 1-6.
[2] Seo UJ, Chun YD, Choi JH, Han PW, Koo DH, Lee J. A technique of torque ripple reduction in interior permanent magnet synchronous motor. IEEE T Magn 2011; 47: 3240-3243.
[3] Lee SK, Kang GH, Hur J, Kim BW. Stator and rotor shape designs of interior permanent magnet type brushless dc motor for reducing torque uctuation. IEEE T Magn 2012; 48: 4662-4665.
[4] Jang SM, Park HI, Choi JY, Ko KJ, Lee SH. Magnet pole shape design of permanent magnet machine for minimization of torque ripple based on electromagnetic eld theory. IEEE T Magn 2011; 47: 3586-3589.
[5] Chu WQ, Zhu ZQ. Investigation of torque ripples in permanent magnet synchronous machines with skewing. IEEE T Magn 2013; 49: 1211-1220.
[6] Yang YP, Lai GY. Design of a permanent magnet motor with SPWM-shaped magnets for an electric scooter. In: 2015 IEEE 24th International Symposium on Industrial Electronics; 3{5 June 2015; Rio de Janeiro, Brazil. New York, NY, USA: IEEE. pp. 476-481.
[7] Upadhayay P, Rajagopal KR. Torque ripple reduction using magnet pole shaping in a surface mounted permanent magnet BLDC motor. In: 2013 International Conference on Renewable Energy Research and Applications; 20{23 October 2013; Madrid, Spain. New York, NY, USA: IEEE. pp. 516-521.
[8] Hwang CC, Wu MH, Cheng SP. In uence of pole and slot combinations on cogging torque in fractional slot PM motors. J Magn Magn Mater 2006; 304: e430-e432.
[9] Wu D, Zhu ZQ. Design tradeoff between cogging torque and torque ripple in fractional slot surface-mounted permanent magnet machines. IEEE T Magn 2015; 51: 1-4.
[10] Zhu ZQ, Howe D. In uence of design parameters on cogging torque in permanent magnet machines. IEEE T Energy Conver 2000; 15: 407-412.
[11] Koh CS, Seol JS. New cogging-torque reduction method for brushless permanent-magnet motors. IEEE T Magn 2003; 39: 3503-3506.
[12] Fazil M, Rajagopal KR. A novel air-gap pro le of single-phase permanent-magnet brushless DC motor for starting torque improvement and cogging torque reduction. IEEE T Magn 2010; 46: 3928-3932.
[13] Petrov I, Ponomarev P, Alexandrova Y, Pyrhonen J. Unequal teeth widths for torque ripple reduction in permanent magnet synchronous machines with fractional-slot non-overlapping windings. IEEE T Magn 2015; 51: 1-9.
[14] Ozoglu Y. New stator tooth for reducing torque ripple in outer rotor permanent magnet machine. Adv Electr Comput En 2016; 16: 49-56.
[15] Hanselman DC. Brushless Permanent Magnet Motor Design. Cranston, RI, USA: The Writers' Collective, 2003.