Research On Characteristic Of Impulse Load Stall And Re-start Of Canned Induction Motor For Vacuum Pump

Pump-type load motors generally adopt open-loop V/F speed regulation control mode,which has poor anti-interference ability.When the motor encounters impact load,the speed of the motor will drop rapidly,so that the pumping speed of the pump will drop and the vacuum degree of the vacuum system will be affected.When the load torque increases to a certain extent,the frequency converter will be trip due to excessive current,causing the motor to lose power.If the converter is restarted directly when the motor rotates,it will cause a secondary impact on the converter and turn it off again.In view of this situation,this thesis designs a canned induction motor for vacuum pump,and studies its stall and restart characteristics under impact load.First,a canned induction motor for vacuum pump is designed in this thesis.The parameters and electromagnetic calculation results of the motor are analyzed by commercial finite element analysis software.After the simulation of the design of the motor under impact load stall and restart characteristics,and the stall and restart characteristic curves of the motor are obtained.Through the analysis of curve,drawbacks of the original motor control system are obtained.Second,because the canned sleeve is added to the canned induction motor,the mathematical model and equivalent circuit of the canned induction motor are different from those of the general induction motor.So,the model of canned sleeve should be equivalent first,and the equivalent circuit model of canned induction motor can be established according to the equivalent circuit model of common induction motor.The mathematical model of the canned induction motor is simplified by coordinate transformation,and then the mathematical model of vector control of the canned induction motor is established according to the way of rotor field orientation.Then,a speed sensorless detection system of canned induction motor is designed by using model reference adaptive method,and the motor speed is estimated.The estimated speed is used as the input of speed feedback and flux observer.Based on the deduced motor model and vector control theory,a speed sensorless vector control system of canned induction motor for vacuum pump is designed.Finally,the feasibility and accuracy of the system are verified by comparing the estimated speed with the actual speed under different conditions.The method of stator residual voltage detection is used to follow the speed of the motor during power failure,which ultimately improves the follow-up of the estimated speed in the process of restarting with speed.Then,by comparing the vector control system with the speed sensor and the V/F speed control system,it is proved that the system has the same control effect as the detection feedback control.Compared with the open-loop V/F control adopted by the general frequency converter,the system has better dynamic characteristics and anti-impact load capability,so that the speed of the canned motor can be maintained in the vacuum system.The stability of the vacuum system can avoid the influence of the suction rate of the vacuum system,and improve the stability of the vacuum rate in the vacuum environment.