Research On Less Stall Control System Of Canned Induction Motor Under The Impact Of Vacuum Pump Direct Discharge Atmospheric

With the progress and development of vacuum technology,the requirements of vacuum production environment in the fields of equipment manufacturing,thin film industry and integrated circuit industry are becoming more and more stringent.Canned induction motor as a vacuum pump drive motor,its on-line running time and stability have been widely concerned by the industry.Aiming at the engineering problem of power failure and stall of canned induction motor caused by the impact of vacuum pump in direct discharge atmosphere,consider the difficult problem of canned motor with restarting with speed and inability to install speed sensor,taking a 4k W canned induction motor as the research object,this thesis makes a specific research on the speed sensorless less stall restart control system of the canned motor under the condition of direct discharge atmospheric of vacuum pump.First of all,a 4k W canned induction motor for vacuum pump is designed in this thesis,and the electromagnetic design,finite element simulation,operation characteristic analysis and stall characteristic analysis are carried out.The variable frequency speed regulation experiment and constant frequency load experiment are carried out on the 4k W prototype.Through the comparison of the results,it is proved that the motor meets the design requirements,and the key points of the design of the canned motor control system under direct discharge atmospheric conditions are determined.Secondly,according to the structural difference between canned motor and ordinary induction motor for vacuum pump,the equivalent circuit and dynamic mathematical model of canned induction motor are established.Based on this model,a speed sensorless control system of shielded motor is established by using model reference adaptive speed estimation strategy.Compared with the traditional open-loop constant voltage-frequency ratio control method of the shielded motor,the simulation results show that the control system has great dynamic stability and impact resistance characteristics,which can effectively ensure the stable operation of the canned motor in the vacuum system and improve the vacuum of the vacuum system.Finally,on the basis of the speed sensorless control system,considering the influence of stator residual voltage after power failure,a speed sensorless residual pressure difference less stall control system is designed.In this thesis,a method of using the state equation of motor motion equation to determine the estimated speed during power failure is proposed,and the analytical formula of residual voltage of canned induction motor stator is derived.A method of simulating the reinput voltage to replace output voltage of the system after power failure is proposed.The characteristics of voltage difference and phase angle difference between simulated reinput voltage and stator residual voltage are simulated and analyzed by using the Hilbert transform（Hibert）function in the residual voltage comparison controller,and the voltage difference amplitude Hibert envelope spectrum is obtained,based on which the first restart area and the secondary restart area are determined.After that,the A-phase power-off residual voltage experiment of 4k W canned induction motor is used to prove the applicability and accuracy of the control method in calculating the residual voltage of canned motor.Through the simulation comparison of direct restart and residual pressure difference restart,it is proved that the residual pressure difference less stall control system can realize low impact,fast and stable less stall restart,it can provide a valuable reference for the less stall restart of canned motor after vacuum pump direct discharge.