Abstract : This paper theoretically analyzes the causes of increased motor noise due to high-order harmonics in the inverter output and fan noise caused by carrier frequency resonance, and proposes solutions. Keywords : noise; fan; inverter; high-order harmonics; carrier frequency During the technical renovation of a boiler room, inverters were used to control the fans, resulting in good energy savings, but the fan noise increased compared to before, with the noise of fan No. 2 becoming particularly loud recently. After on-site inspection and testing, the analysis results showed that the noise of fan No. 2 was caused by the carrier frequency output by the inverter being the same as the fan's vibration frequency (resonance), while the increased noise of other fans was caused by high-order harmonics in the inverter output. This paper theoretically analyzes the causes of increased noise in fan No. 2 and other fans and discusses solutions. 1 Inverter Output Carrier Frequency and Fan Noise During the inspection, it was found that the root of the fan blades of fan No. 2 had slight cracks due to mechanical fatigue, causing the overall vibration frequency of fan No. 2 to be exactly the same as the inverter's output carrier frequency. Other fans did not exhibit this phenomenon. The frequency converter used in the wind turbine is a Pulse Width Modulation (PWM) transistor frequency converter. PWM transistor frequency converters are a widely used type of frequency converter. PWM control is a control method that simultaneously controls the amplitude and frequency of the output voltage (current) in the inverter circuit. In this control method, the switching of semiconductor switching components in the inverter circuit is controlled at a relatively high frequency, and the voltage (current) is controlled by changing the width of the output pulse. The carrier frequency determines the number of PWM pulses in the frequency converter's output voltage (current), which indicates the quality of the output waveform; the higher the carrier frequency, the better the output voltage (current) waveform. To make the asynchronous motor run more smoothly during speed regulation, sinusoidal PWM control is now widely used in frequency converters. Sinusoidal PWM control refers to changing the pulse width of the PWM output to make the average value of the output voltage close to a sine wave. This control method is simple and low-cost, but it can generate significant motor noise when the carrier frequency is inappropriate. [b][align=center]For detailed information, please click: Theoretical Analysis and Solutions for Fan Noise[/align][/b]