Harmonic Harm And Suppression Of Canned Motor Speed Control System For Vacuum Dry Pump Drive

Canned motor for driving vacuum dry pump,as a product of the combination of vacuum application technology and variable frequency speed regulation technology,has unique advantages.However,due to the existence of the variable frequency speed regulation system,there are a large number of time harmonics in the motor current,which will have a great impact on the performance of the motor.Therefore,this paper takes a 1.5k W permanent magnet canned motor as an example to discuss the control system,harmonic suppression and the influence of harmonic on the motor.In this paper,a mathematical model of a 1.5k W permanent magnet shielded motor is established,and the control system of the motor is simulated.The simulation results are compared with the experimental results to verify the correctness of the simulation.Then design a shunt active filter,place the active filter in the motor control system to suppress current harmonics,and analyze the performance of the motor before and after filtering.First of all,a mathematical model of the motor is established for the difference between the structure and operation mode of the canned motor for driving the vacuum dry pump and the conventional AC motor.And a closed-loop vector control system suitable for the motor is established.The vector control system of the motor adopts the SVPWM modulation method.The working characteristics of the motor are analyzed and compared with the experimental results of the prototype,which proves the correctness of the simulation.Then,in order to be able to suppress the harmonics under the dynamic load of the shielded motor,Active power filter for vacuum pump drive is designed.First,the principle of the active filter is introduced,and the i_p-i_q harmonic detection method based on the instantaneous reactive power theory is analyzed in detail.Subsequently,the control strategy of the parallel active power filter is analyzed,the control strategy of the triangular wave comparison method is determined to control the compensation current,and the closed-loop control method of the DC side voltage is determined.According to the design plan,the active filter is simulated in Matlab/simulink,and then the active filter is connected in parallel to the inverter output of the motor control system to suppress the harmonics of the inverter output current.By comparing the current harmonic distortion rate before and after the filter connection,the correctness of the active power filter design is proved.Finally,the shielded motor is simulated in the finite element software,and the current before and after filtering obtained in Matlab/simulink is used as the current excitation of the finite element simulation software.The effects of harmonics on the stator and rotor losses of the motor and the eddy current losses of the shield sleeve and permanent magnets are discussed.