Research On Key Technology Of High Vacuum Molecular Pump Drive

A high vacuum molecular pump is a mechanical pump that rotates very fast and is the main equipment for obtaining a clean ultra-high vacuum environment.The molecular pump is started in a low pressure environment and the rated speed reaches tens of thousands of revolutions per minute,so the drive system of the molecular pump directly affects the working performance of the equipment.In this paper,we study how to choose the power source of molecular pump,the improvement of rotor pre-positioning,position detection method and drive method of molecular pump drive motor.Based on the comprehensive consideration of equipment working requirements and cost,the permanent magnet brushless DC motor without position sensor is chosen as the power source for the small composite molecular pump used on the low particle valve particle size inspection platform,and the control strategy and rotor position detection method of the motor are studied.The control strategy and rotor position detection method of the motor are studied,which are important for improving the engineering application value of the molecular pump.The details of the study are as follows.（1）Based on the mechanical structure and pumping principle of the molecular pump,the subject studied the load characteristics of the molecular pump during the start-up,acceleration and stable operation stages,and the results showed that the frictional resistance and air resistance of the molecular pump are very small when it works,and the motor torque is mainly used to provide acceleration;then,combined with the working requirements of the molecular pump,the load characteristics and the advantages and disadvantages of different kinds of motors,the types and parameters of the molecular pump drive motor were determined（2）According to the selected BL motor,the driving performance can be obtained.（2）According to the structure and operating principle of the selected permanent magnet brushless DC motor（BLDCM）,the project determines the suitable motor starting,accelerating and stopping methods: in the starting stage,the software boosting method is used,which reduces the workload compared with the traditional hardware boosting method;in the accelerating stage,the double closed-loop PI control of speed and current is used,which can limit the current and ensure the smooth rise of speed and the safety of the motor In the stopping phase,the energy braking method is used to reduce the deceleration time of the molecular pump.（3）The subject proposes an improved rotor position prepositioning method and a line counter potential over zero method for rotor position detection in the acceleration phase: the specific motor winding is energized twice in the prepositioning to ensure that the motor rotor is dragged to the set position and to well avoid locking of the motor rotor;the line counter potential method is used in the acceleration phase by measuring the motor phase voltage,phase resistance,and Phase current is calculated to obtain the phase change point.Compared with the traditional opposite potential over zero method,the step of delaying the electrical angle is omitted,which reduces the driving cost and improves the stability of phase change.This project also verifies the validity of the line opposite potential over zero method and the renewal of the current in a phase that is suspended and not energized when the stator magnetic field does not jump.（4）Finally,the main hardware circuit and software control system of the molecular pump driver are designed and fabricated,including the design of the schematic diagram and the selection of main components,the design and fabrication of the PCB board,the soldering and debugging,and the writing of the controller code.The test platform of BLDCM was also established in this project to verify the related control methods.Finally,the control debugging of the molecular pump was realized on the particle size testing platform.