Research On Control Strategy Of High Speed Brushless DC Motor Based On Line Back EMF

Brushless DC motor(BLDCM)is a kind of mechatronics equipment which can be realized with the development of power electronics technology and microprocessor technology.Because it combines the characteristics of simple structure of AC motor and excellent speed regulation performance of DC motor,BLDCM is gradually applied in various fields.The traditional brushless DC motor control technology uses position sensor to detect the rotor position to control the main part of the AC motor to commutate.In contrast,the newly emerging brushless DC motor speed control system without rotor position sensor has the advantages of small size and high accuracy.This thesis will mainly analyze the control of high-speed brushless DC motor without position sensor and design an optimized control system.Firstly,the research status of brushless DC motors in high-speed,positionless sensor detection methods,rotor position correction methods and control algorithms is analyzed.Based on the mathematical model of brushless DC motors,brushless DC motors are further analyzed.The reason,suppression method and Pulse Width Modulation(PWM)conduction method of motor torque ripple.Then,starting from the mathematical model,the rotor position correction method based on back electromotive force sum and the rotor current correction method based on phase current are proposed,and the design scheme of Proportion Integral(PI)for rotor position correction based on phase current is also given.And verified the correctness of the proposed method and design scheme.Secondly,in-depth analysis of the three-three conduction and two-two conduction methods in the brushless DC motor control method,on the basis of studying the position detection method based on terminal voltage and phase voltage,propose a new position detection method based on line back-EMF,the position detection method of this method is used to simulate the brushless DC motor non-inductive control system using this method.The simulation results verify the correctness and superiority of the overall design scheme.By comparing the back-EMF,current and torque waveforms,the results are further verified Improve the robustness of the correction method.Finally,the design scheme of the sensorless brushless DC motor control system based on line back-EMF force is given.With TMS320F28335 as the core main control chip,on the basis of the structural block diagram of the control system design,the hardware of each part of the system is designed.The circuit and the flow chart of the control program of the high-speed brushless DC motor based on line back-EMF detection are given,which verifies the feasibility of the sensorless control system of the high-speed brushless DC motor.