Magnetic noise reduction technique for an AC motor driven by a PWM inverter

A technique for reducing magnetic noise from an AC motor driven by a pulsewidth modulation (PWM) inverter is proposed. In this technique, the meaningless magnetic noise is converted into selected information. The technique can be adopted independently of the inverter rated output power. The relationship between carrier waveform frequency in PWM control and harmonics contained in the motor current is first clarified by a harmonics analysis. Then a hardware circuit configuration and carrier frequency control software in a microcomputer are introduced. Using a musical melody as the selected information, the effect of this control is experimentally confirmed. It is shown that the desired sound can be obtained from the AC motor, and the motor voltage and motor current waveforms are not affected by such control