Direct Torque Control Of Sensorless Brushless DC Motor

Compared with other motors,Brushless DC motor has the advantages of simple structure,large output and high efficiency,so it is widely used in various fields.But the position sensor increases the volume of Brushless DC motor,and effects the influence of detection under the high temperature environment,so the Sensorless technology is the focus of the present research.At the same time,the traditional Direct Torque Control technology is applied to the Brushless DC motor,torque ripple problem still exists,so the suppression of torque ripple is also the focus of current research.Firstly,through the basic structure of the Brushless DC motor,the working principle,mathematical model,transfer function and characteristic curve of the motor are analyzed.In order to overcome the disadvantages of the existing Sensorless technology,a new method based on the line voltage difference method is developed to detect the back EMF zero crossing signal.At the same time,the Brushless DC motor cannot detect the back EMF signal in the start-up phase,so that the motor is difficult to start,through the study of the three stage start method to solve the problem of the Brushless DC motor starting.And the simulation model of Sensorless DC motor is built in Matlab/Simulink,the simulation results show that the correctness of the method of the line voltage difference and the three stage method.Secondly,there has a problem that the computational complexity of flux linkage observation in the traditional Direct Torque Control.According to the characteristics of Brushless DC motor,the relationship between voltage vector and torque is studied under the condition that the flux observers is ignored,and the optimal voltage vector switch table is obtained on the basis of the relationship between them.In view of the traditional Direct Torque Control still exists the problem of torque ripple,the Direct Torque Control technology based on the optimal duty cycle is studied.In this method,the torque ripple is reduced by adjusting the duty cycle of the optimal voltage vector in a sampling period,the remaining time of sampling period is effect by zero voltage vector.And the simulation model of Direct Torque Control of Brushless DC motor is built in Matlab/Simulink.By comparing the simulation waveforms of traditional Direct Torque Control and improved Direct Torque Control,the simulation results show that the Direct Torque Control technology based on the optimal duty cycle can reduce the torque ripple.Finally,the hardware and software of the Brushless DC motor are designed based on TMS320F28335.And through the experimental waveforms are analyzed,the results show that the proposed control strategy is correct.