Research On Shaft Voltage Analysis And Suppression Method Of Outer Rotor Magnetic Field Modulation Moto

Flux-Concentrating Field-Modulated Permanent Magnet(FCFMPM)is a permanent magnet motor based on the principle of magnetic field modulation,which has the characteristics of low speed and high torque,and has significant advantages in lowspeed direct drive applications.However,when using the inverter drive control,the commonmode voltage generated by the inverter induces the shaft voltage on the shaft through the parasitic capacitance inside the motor.The excessive shaft voltage causes the bearing oil film to be broken down to generate a short-circuit current,releasing heat to melt the metal near the breakdown point,thereby causing electrical corrosion to the bearing.Electrical corrosion will shorten the service life of bearings,so that the bearings of the motor have to be replaced frequently,which increases the time cost,material cost and labor cost of the project.In severe cases,it can cause damage to the motor,bring huge economic losses,and even casualties.In this paper,the shaft voltage problem of FCFMPM motor driven by inverter is studied.Through the simulation analysis of the equivalent circuit model of shaft voltage,the waveform and amplitude of shaft voltage under different breakdown states of bearing are predicted.Then the simulation results are verified by experiments.Finally,some solutions are proposed for the shaft voltage problem of the motor.The main work of this paper includes the following aspects:1.Firstly,the generation mechanism of common mode voltage is introduced,and then the equivalent circuit model of shaft voltage of FCFMPM motor is established.Then the equivalent circuit model of shaft voltage is improved appropriately,so that it can analyze the shaft voltage when the bearing has breakdown.Finally,the parameters required in the shaft voltage equivalent circuit are calculated by finite element and analytical methods.2.The common mode voltage and shaft voltage of the bearing under different breakdown states and different breakdown delays of the bearing are simulated in Simulink for the proposed improved shaft voltage equivalent circuit;According to the simulation modeling results,the influence of bearing breakdown delay and bearing breakdown number on shaft voltage value is obtained;Then,by analyzing the relationship between the number of bearing breakdowns and the amplitude of the shaft voltage,the range of the amplitude of the shaft voltage is estimated.3.The shaft voltage experimental platform of FCFMPM motor is built,and the shaft voltage test is carried out through the platform.The waveform obtained by the experimental test is compared with the simulation waveform to verify that the improved shaft voltage equivalent circuit model can reflect the shaft voltage waveform of the motor.By comparing the shaft voltage amplitude tested by statistical experiments with the estimated value range,it is verified that the model can estimate the value range of the shaft voltage.4.Based on the shaft voltage equivalent circuit model and the shaft voltage divider ratio formula,the shaft voltage suppression method of the motor is analyzed;the influence of air gap length and pole shoe width on shaft voltage in motor structure parameters is analyzed by parametric scanning method.Finally,without changing the structural parameters of the motor,other suppression methods are proposed for the characteristics of the motor,and the suppression effect of each suppression method on the shaft voltage is obtained through simulation analysis.