Reduced harmonics PWM controlled line-side converter for electric drives

The concept for a reduced-harmonics PWM modulator, as applied for the control of a line-side power converter for a variable speed AC motor drive, is described. The PWM algorithm determines the on-state duration of each switching vector based on the observation of the time-variable voltage reference vector. Since there is no reference made to a constant-frequency carrier signal, the generated pulse patterns become asynchronous. It is the essential property of this method to produce a quasicontinuous harmonic spectrum in which all frequency components have more or less equal magnitudes. This is an advantage as compared with carrier-based PWM control schemes that exhibit high-amplitude carrier and side-band components in their harmonic spectra. The emission of acoustic noise radiated from the AC filter inductor is reduced