Research And Implementation Of Sensorless Control System For Brushless DC Motor

Brushless Direct Current Motor(BLDCM)has great potential in the field of electric drive because of its high efficiency and energy saving.BLDCM control system needs the position sensor installed inside the motor to provide rotor position information,which is used for commutation during normal operation of the motor.However,the installation of position sensor inside the motor will increase the size and cost of the motor,and increase the difficulty of manufacturing and maintenance.Therefore,the application of Sensorless control technology in BLDCM control system is now a research hotspot.This paper studies a new method of BLDCM rotor position detection: zero crossing detection method of terminal voltage comparison during non conduction phase PWM,and explores the fast start process applied to this method.Based on the completion of hardware design and software design,the feasibility and stability of the above method are verified:(1)Firstly,the working principle and mathematical model of BLDCM are analyzed.On this basis,five kinds of PWM modulation modes in two-on mode are analyzed;(2)In the process of motor commutation,based on the analysis of the shortcomings and shortcomings of the traditional back EMF zero crossing detection method,a zero crossing detection method of terminal voltage comparison during non conduction phase PWM is adopted.This method does not need to filter the terminal voltage,so it will not cause phase delay in the process of commutation,and can detect the back EMF zero crossing signal more accurately;(3)Motor starting is a difficult point of BLDCM sensorless control.This paper introduces two starting methods.First,it analyzes the starting method based on short-time pulse detection,which can ensure the reliable starting of motor.Then,it introduces a fast starting method based on two conduction states,which is characterized by overcoming the problem of slow speed of traditional three-stage starting,and the electric motor can be started reliably It can reach the given speed quickly;(4)The hardware design of BLDCM sensorless control system includes STM32F103C8T6 peripheral circuit,power supply circuit,full bridge inverter circuit and its driving circuit,back EMF zero crossing detection circuit,auxiliary circuit and protection circuit;(5)Based on IAR development environment,the software design of sensorless control system is completed.Firstly,the main program and interrupt service program in the software design are analyzed,and then the design of each subprogram is described in detail.Finally,an experimental platform is built to verify the proposed method,and the output waveform and speed response waveform of the comparator are analyzed,which fully illustrates the feasibility of zero crossing detection method of terminal voltage comparison during non conduction phase PWM and fast start method based on two conduction states.