Research On High-speed Permanent Magnet Brushless DC Motor And Control System

With the advantages of high speed,small volume,high power density,fast transient response and high efficiency,High-speed permanent magnet brushless DC motor(BLDC)is applied in high speed field more and more widely.Generally,the operation of BLDC must be controlled by control system,because more and more disadvantages is present in the terrible field using BLDC with position sensor,in recent years,brushless DC motor without position sensor technology is being hot.The research on high-speed permanent brushless DC motor is applied to the small molecular pump,it is a kind of vacuum pump,the rigid body with high-speed rotation transfer energy to gas molecules,then the gas molecules will flow in a fixed direction,so we can get the vacuum environment.Due to the reason of the high-speed motor lying in the molecular pump and the normal working environment being closed vacuum,which brings much difficulty to the cooling of motor.In addition,the project only allow 20 Celsius temperature rise,so the key of research is to cut back the loss of motor.Therefore,we take much measures to reduce the heat loss of motor in the design of BLDC.At last,we prove that the design satisfy the demand of molecular pump.In terms of motor control,for improving motor efficiency,reducing motor torque fluctuations,improving motor performance.based on the characteristics of the winding neutral point voltage change under different PWM chopping modes and the freewheeling phase of the non-conducting phase winding under different PWM chopping modes.To ensure that the motor is commutated at the "optimal commutation point",in the base of high-speed permanent magnet brushless DC motor position sensorless control system with Terminal voltage detection circuit and H-PWM-L-PWM Driving method,we put forward the close-loop phase correction method based on the midpoint voltage of non-conducting phase.After using this method,Commutation error and torque ripple are greatly reduced,which improves the stability of the motor operation?Then,we proved that this method is effective and feasible,which improves motor's reliability and stability.For the problem of high-speed motor startup problem,we put forward improved software startup method on the basis of traditional hardware startup method,which makes motor start without hardware circuit.And the starting step and the starting voltage can adjust at any time by upper computer,which enhances the robustness of control system.In addition,PI regulation was added during the stage of motor speed rising,and limit Winding voltage by software,which can not only make the motor speed rise smoothly but also avoid excessive winding current,this greatly reduce the chance of motor out-of-step and increase the success rate of start-up.At last,on the base of above study,with dsPIC30F3011 as the main control chip,we designed and developed a high speed permanent magnet brushless DC motor position sensorless control system based on "terminal voltage method",which can realize the real-time control and status monitoring of the motor through the RS485 serial port communication.Test proved,The system can operate safely and meet the control requirements of small molecular pumps reliably...