REDUCTION OF TORQUE RIPPLE IN BRUSHLESS DC MOTORS

For permanent magnet (PM) brushless DC motors, torque ripple, is an im portant origin of vibration, acoustic noise and speed fluctuation. In this paper, the output torque profile of a PM motor with one phase ene rgized is decomposed into the commutation torque, the reluctance torqu e and the armature reaction according to their source origins. It veri fies that the output torque profile is qualitatively equivalent to the BEMF profile for low reluctance motors. This paper discusses the effe ct of magnet pole shaping and magnet are length on the output torque a nd torque ripple. A magnet edge shaping is proposed to design a trapez oidal BEMF motor without torque ripple, with minimal sacrifice of the maximum output torque.