IEEE TRANSACTIONS ON MAGNETICS, VOL. 50, NO. 2, FEBRUARY 2014 

Sun-Kwon Lee1,2, Gyu-Hong Kang1, Jin Hur2, and Byoung-Woo Kim2 

This paper deals with the reduction of torque pulsation including torque ripple and cogging torque in surface PM brushless

ac motors. The fractional combination and air-gap shape design by shaping the PM and stator core are studied to reduce torque

pulsation. Torque ripple reduction is achieved by adjusting the magnetic flux density in air-gap contour by cutting magnet outer

shape. Quasi-zero torque pulsation in this paper means the ripple ratio to average torque <0.5%. The magnetic field and torque

characteristics are analyzed by 2-D finite element analysis and prototype to validate is manufactured and measured.