Research On Torque Ripple Minimization Techniques For Permanent Magnet Brushless DC Motor

Permanent magnet brushless DC motor has good mechanical properties and speed control performance,wide speed range and higher power density virtues,so it can be applied in many fields.In recent years,with the development and breakthrough of the technology of rare earth permanent magnetic material and power electronics,the application and development of permanent magnet brushless DC motor in the wider field is promoted.However,the torque ripple is an unavoidable problem for the permanent magnet brushless DC motor.Because of the existence of the torque ripple,the application of the permanent magnet brushless DC motor in some high precision position and speed control system has been limited.The commutation torque ripple occupies a large proportion of the torque ripple,and even reached 50%of the average torque of the permanent magnet brushless DC motor.So it is a hot issue for researchers at home and abroad that it is the problem of torque ripple for permanent magnet brushless DC motor,especially the suppression of commutation torque ripple.The basic structure and operating principle of the permanent magnet brushless DC motor are analyzed in detail in this thesis,and on this basis,pushing derived permanent magnet brushless DC motor mathematical model;The simulation model of the permanent magnet brushless DC motor control system is built on the Matlab/Simulink platform,and the simulation modules are briefly introduced,and the simulation experiment is done with the double closed-loop control strategy,and the correctness of the designed control system is verified.In this thesis,the cause of the torque ripple caused by the anti parallel diode continued flow during the non commutation phase is theoretically expounded.Moreover,the theoretical analysis and simulation of the torque ripple of different PWM modulation modes are studied.The conclusion is that the torque ripple of the non-commutation region can be effectively suppressed by pwm-on-pwm modulation.In this thesis,the commutation torque ripple of mechanism from different aspects are discussed,by using mathematical formula,analysis the influence of several common used PWM modes on commutation torque ripples in different degrees.This thesis propose a method to reduce and minimize commutation torque ripple:when the motor in low speed state,the use of pwm-on-pwm modulation mode can well inhibit the commutation torque ripple effect;In high speed state,on the basis of pwm-on-pwm modulation using commutation torque ripple compensation control strategy,namely in the set for phase compensation time,keep the opening phase of open all the time,by controlling the turn off phase modulation for empty ratio to inhibit the commutation torque ripple.In order to verify the proposed theory,the control system of permanent magnet brushless DC motor with CPLD&DSP control chip is designed,and the hardware design and software design of the controller are accomplished.The experimental analysis and research show that the control strategy can better suppress the torque ripple of permanent magnet brushless DC motor in the low-speed region and the high speed region.