Abstract
In recent years, due to the benefits of high efficiency and saving energy, induction motors fed by inverter have been widely used. Because of the distorted output waveform of an inverter, the magnetic noise emitted from the motor is becoming a serious environment problem. To reduce the magnetic noise, the harmonic current must be depressed. Raising the switching frequency of an inverter is a very efficient method to reduce the harmonic current, but it can only be used for high switching speed devices like IGBT's, and another problem of switching loss occurs as the switching frequency is raised.
This paper proposes a new PWM method that can be used to reduce the harmonic current. The integrated area of the differences between the locus of ideal flux vector and the actual flux vector can be considered as the total harmonic current RMS value. The proposed new PWM method determines the vector output timing to let the integrated area to be minimum. For the evaluation of low acoustic magnetic noise, the motor acoustic magnetic noise vs. harmonic current characteristic curve is defined, and a new kind of acoustic magnetic noise evaluating method based on this characteristic curve is proposed. At the end of this paper, the experimental results are shown to verify the effectiveness of the proposed method.
