The motor factory-motor manufacturer reminds that the main reason for the high-frequency shaft current of the frequency conversion speed control motor is that the power frequency three-phase sinusoidal power supply voltage is balanced and symmetrical. Therefore, the neutral point voltage is zero, but the frequency converter affects the frequency conversion. The output voltage of the speed regulating motor is generated by PWM pulse width modulation, that is, the DC voltage is converted into a three-phase sinusoidal exchange voltage through the inverter.

　　Although the fundamental frequency component is symmetrical and balanced, the switching of the diode in the inverter unit cannot be absolutely synchronized. Therefore, the output current of the variable frequency speed control motor has high-order harmonics, which causes the voltage component to increase. Large, that is, the neutral point voltage is not zero.In the standard, this zero-sequence voltage is defined as a common-mode voltage. This voltage can be measured at the neutral point in the load motor winding. Its frequency is communicated with the breaking frequency of the diode in the inverter unit, and its amplitude is the same as that of the DC bus. The voltage is proportional.The scale defines that the shaft current generated by the common mode voltage is called the high-frequency shaft current.