The high-order harmonics which have great influence on vibration are mainly lower harmonics, which have great influence on PAM mode and square wave PWM mode. However, when using sine wave PWM mode, the low order harmonic component is small and the influence is smaller. When the motor is driven by frequency converter, the output voltage and current contain higher harmonic components, and the higher harmonic flux of air gap increases, so the noise increases. The electromagnetic noise has the following characteristics: because the low order harmonic component in the inverter output resonates with the natural mechanical frequency of the rotor, the noise near the natural frequency of the rotor increases. The higher harmonic components in the output of the frequency converter resonate with the bearing frame of the iron core housing, and the noise increases near the natural frequencies of these components. The noise, especially the harsh noise, produced by the inverter drive motor is related to the switching frequency controlled by PWM, especially in the low frequency region. If the frequency converter is used to adjust the speed, the noise and vibration will be produced, which is caused by the high-order harmonic component in the output waveform of the frequency converter. With the change of operating frequency, the fundamental and higher harmonic components change in a large range, which may cause resonance with various parts of the motor.

Vibration and noise treatment methods to reduce or eliminate vibration, AC reactor can be connected to the output side of the inverter to absorb the high-order harmonic current component in the inverter output current.

When PAM or square wave PWM converter is used, sine wave PWM converter can be used to reduce the pulsating torque. In order to prevent the vibration of the mechanical system connected by the motor and the load, the whole system must not be resonant with the electromagnetic force produced by the motor. Generally, the following measures are adopted to suppress and reduce noise: connect AC reactor at the output side of frequency converter. If the electromagnetic torque has margin, U / F can be set smaller. If a special motor is used, the resonance with the natural frequency of the shaft system (including the load) should be checked if the noise volume at the lower frequency is serious