Research And Design Of Brushless DC Motor Sensorless Control System Based On DSP

Permanent magnet brushless DC motor is a kind of small power DC motor,its most prominent feature is the abolition of the mechanical commutation device,instead of using electronic commutation device to complete the winding commutation process.Electronic commutator generally refers to the three-phase full-bridge inverter which consists of the semiconductor power switch tube.The motor windings achieve commutation through the control of each switch in the inverter to be on and off,replacing the mechanical commutation method.This kind of motor has many advantages,such as simple structure,reliable operation,high working efficiency,strong overload capacity and low electromagnetic noise.It is widely used in industrial and agricultural production,national defense,spaceflight and automobile.Up to now,most brushless DC motors in the market use position sensors to obtain the rotor position of the motor.However,it is found in the using that it will result in commutation error because this method will appear large signal detection error when the position sensors work in harsh environment such as high temperature and high humidity.Based on this background,the control method without position sensor is proposed,that is,the research and design of the position sensorless control system.In this thesis,it takes three-phase four pairs of poles permanent magnet brushless DC motor as the object to study.Firstly,this thesis introduces the development situation of BLDCM and its control technology both at home and abroad,and analyzes the need to study the brushless DC motor control system.It introduces the basic structure and working modes,then selects the two and two conduction mode through the comparison of different working ways.At the same time,for the common phenomenon of brushless DC motor torque ripple during high speed operation,this thesis uses a predictive current control strategy.In order to solve the problem of initial position detection of rotor in the sensorless control system,the inductance identification method is adopted.The improved three-stage starting method is adopted in the starting process,and the line back electromotive force method is adopted to solve the commutation problem based on the research and analysis.Secondly,the double closed-loop control system without position sensor is built by MATLAB/Simulink simulation platform.The simulation of the motor self-synchronization acceleration,external synchronization acceleration and predicting current control strategy is carried out and the feasibility of the control system is verified by system simulation.Finally,after the feasibility of the sensorless control method is verified by simulation,the hardware circuit and the software program of the control system are designed.Through the experiments of motor starting,accelerating and steady running,the zero-crossing signal of the back electromotive force and the current signal and the driving signal are observed by the oscilloscope.The experimental waveform is analyzed and the feasibility of the method is proved.