Research On Control Method Of Sensorless Brushless DC Motor With Low Torque Ripple

In recent years,brushless DC motors have been widely used in many applications because of the development of power electronics technology,inverter control technology and new permanent magnet materials.However,position sensors of brushless DC motors increase the cost and volume of the motor and reduce the reliability of motors,torque ripple is an inherent disadvantage during the operation of the brushless DC motor.Therefore,the sensorless control technology of the brushless DC motor and the suppression of torque ripple have important theoretical research value.This paper mainly studies the position sensorless control system of brushless DC motor,and further realizes the operation of low torque ripple of brushless DC motor.Firstly,this paper introduces the research status of rotor position detection method and starting method for position sensorless control of brushless DC motor,and introduces the main methods to reduce the torque ripple of brushless DC motor in China and abroad.The working principle of self-synchronous operation under rotor initial position detection,acceleration start and rotor position detection based on terminal voltage is described in detail.The simulation model is built in Matlab/simulink.Secondly,because the magnitude of electromagnetic torque fluctuation is related to the accuracy of rotor position detection in the absence of position sensor control.Therefore,aiming at the problem of commutation error in the position sensorless control of brushless DC motor based on terminal voltage,the delay position of the rotor position detection caused by the filter circuit is compensated by adopting the delay compensation strategy of‘90~?-?'.Aiming at the other factors causing the motor rotor detection error,by analyzing the characteristics of the phase current change caused by the error of the rotor position detection,it is proposed to equalize the non-commutated phase current integrals in the range of 30°before and after the commutation.The integral difference of the phase current is used as the feedback amount,the phase of the commutation signal is corrected by PI adjustment.Based on the two methods,a closed-loop control method for correcting the error of the positionless commutation signal is proposed.The effectiveness of the rotor position correction method is verified by simulation.Then,by comparing the six commonly used PWM modulation methods of the two-wire conduction of the brushless DC motor,the PWM modulation method that minimizes the commutation torque ripple of the brushless DC motor is obtained.In the aspect of torque pulsation suppression in the commutation area of the system,the problem that the speed of the current rise during the turn-on period of the motor commutation period and the speed of the current drop during the turn-off period are inconsistent.A new type of voltage switching circuit based on SEPIC converter is added on the DC side of the main circuit of the power converter,through the analysis of its control method,when entering the commutation area,the DC bus supply voltage is maintained at four times the motor back EMF voltage,and the torque pulsation suppression effect of the commutation area of the system is verified by simulation.Finally,the FPGA-based brushless DC motor control system is designed,including the design of the hardware circuit and the design of the software control module,build the experimental platform and debug it.The experimental results verify the feasibility and effectiveness of the brushless DC motor control system with FPGA as the controller.