Research On Torque Ripple Characteristics Of Braking Modulation Methods Of BLDCM

Brushless DC motors have the advantages of high power density and high efficiency,therefore they are widely used in aerospace,electric vehicles and other fields.The motor will produce torque ripple under braking conditions,and the torque ripple will bring about problems such as resonance and noise.These problems seriously affect the stability and reliability of the brushless DC motor,and limit the application of the motor in some high precision and high stability occasions.Based on the mathematical model of brushless DC motors,the six braking modulation methods,the four-quadrant operation and the working principle of feedback braking are mainly analyzed.Due to the different braking modulation methods,the braking current flow path in the three-phase full-bridge circuit is vary,and thus the torque ripple generated is also different.In the non-commutation interval and the commutation interval,the mathematical expressions of the non-commutation torque ripple and the commutation torque ripple of the different braking modulation modes are respectively derived,and the characteristics of torque and current of the different modulation modes are analyzed and compared through the expressions.The brushless DC motor simulation model is built in MATLAB/Simulink environment,and the simulation research of the motor speed,torque,current and other characteristics is carried out.According to the functional requirements of the control system,the hardware circuit and software program of the control system are designed in sub-modules,a test platform of the brushless DC motor is built,and the experimental research on the characteristics of the motor speed and current is carried out.In this paper,a unified mathematical derivation and comparative study on the torque ripple of six common braking modulation methods are carried out.The non-commutation torque ripple and the commutation torque ripple are analyzed.The following conclusions can be obtained through theoretical deduction,simulation and experimental verification:(1)In the non-commutation interval,the PWM_OFF_PWM and H PWM-L_PWM modulation methods do not have non-commutation torque ripple caused by non-conducting phase dynamic freewheeling,while the other four modulation methods have non-commutation torque ripple caused by non-conducting phase dynamic freewheeling.(2)In commutation interval,PWM_OFF_PWM modulation method is used as an example.The commutation torque ripple suppression method is compared with conventional PWM_OFF_PWM method can effectively reduce commutation torque ripple.(3)In this paper,the analysis and derivation of the mathematical expressions of the torque ripple of different braking modulation methods provide a theoretical basis for seeking a better PWM modulation method.