Brushless Dc Motor Torque Ripple Suppression Method

Due to the replacement of mechanical commutation by electrical commutation,the permanent magnet brushless DC motor(BLDCM) is simple in construct,reliable in performance and convenient in maintenance as AC motor,and features as traditional DC motor in speed control.But there is ripple in torque output of BLDCM when BLDCM is working in non-commutation state and commutation state.These disadvantages of BLDCM prevent the application of BLDCM from some fields,especially in accurate motor drive.This paper introduces the basic principle of three-phase BLDCM in first and designs simulation modules with MATLAB/Simulink according to BLDCM's principle.Five traditional types of Pulse Width Modulation (PWM) of BLDCM drive are analyzed on non-commutation state and commutation state.Performances of these types of PWM are evaluated by simulation with Matlab.Then,this paper introduced and studied the PWM_ON_PWM type of PWM.Simulation with Matlab indicates that PWM_ON_PWM type is better than other traditional types of PWM in reducing torque ripple during non-commutation state of BLDCM.Although the application of PWM_ON_PWM type of PWM in BLDCM drive can restrain torque ripple in non-commutation state of BLDCM,Pulse Width Modulation can make inevitable torque ripple which is not expected in certain situations.An approach to make the torque of BLDCM smooth by using Buck DC-DC converter in topology of drive is introduced in this paper.This paper also provides an approach based on Buck DC-DC converter to reduce the torque ripple during commutation state of BLDCM.Simulation with Matlab indicates that this approach is right and usable.