Influence of Keybar-slot on Torque Characteristics of Direct-Drive Permanent-Magnet Brushless Machines

The keybar-slots are inevitable and necessary for the installation of torque motor used for CMG (Control moment gyro) for the satellite This paper investigates the influence of keybar-slot on torque characteristics of direct-drive permanent-magnet brushless DC (PM BLDC) motor. The model and specification are illustrated. Then the keybar-slot effects on torque characteristics are analyzed through finite element analysis (FEA). It shows that high localized magnetic saturation due to stator asymmetry can significantly increase cogging torque and torque ripple. An effective method has been proposed to improve the asymmetry by applying five uniformed distributed keybar-slots in the stator yoke.