High-Speed Permanent Magnet Motor Shaft Voltage Analysis Method Based On Capacitance Network

With the wide application of high-frequency switch,frequency conversion technology has become very common,and is currently widely used in industrial fields such as industrial control and energy conversion.When the motor is working,the three-phase voltage of the PWM inverter’s instantaneous output is asymmetrical,and a common mode voltage is generated in the system.The common mode voltage will cause the shaft voltage,which causes a voltage drop between the shaft end and the ground,affecting the safety of the motor.Based on the research purpose of reliable operation of high-speed motor,this paper analyzes and studies the shaft voltage of high-speed motor based on capacitor network.Firstly,in order to accurately analyze and calculate the value of the shaft voltage,the internal capacitance network of the high-speed permanent magnet motor is established,and the capacitance is calculated numerically,finite element calculated and experimental measured.After verifying the accuracy of the model,the model was used to analyze the influence of some motor parameters such as motor air gap length,slot width,and slot height on capacitance.Secondly,the common mode voltage and shaft voltage of high-speed permanent magnet synchronous motors are analyzed by establishing a common mode model.During the analysis,the possible effects of the sheath and the winding end on the model are considered.Based on this model and the analysis of the influence of some motor parameters on the capacitance,the influence of the motor parameters on the shaft voltage is analyzed,and the influence of some motor driver parameters such as DC bus voltage on the shaft voltage is further analyzed.Then,based on the capacitance network model,the shaft voltage suppression method is analyzed.The grounding copper conductor is used to simulate the suppression effect of the shaft voltage,and the analysis of the influence of the thickness of the copper conductor on the suppression effect of the shaft voltage is emphasized.For the motor after the installation of the grounded copper conductor,under the condition of a certain amount of current harmon ics,the study of the change law of the motor loss is carried out.Then,the motor temperature field analysis model is established to study the temperature rise of the grounded copper conductor installed in the motor.Finally,on the basis of the common-mode model of the motor,the law of the power level on the motor shaft voltage is explored,and the effect of the medium on the shaft voltage in the environment of the motor fully immersed in liquid oxygen and liquid hydrogen is studied.Then,under the condition that the chassis grounding form is different,the change law of the motor shaft voltage is analyzed,so as to realize the safe and reliable operation of the motor.