Analytical predetermination of complex line-current harmonics in controlled AC/DC converters

When predetermining complex line-current harmonics of controlled converters, the effects of commutation and DC ripple must be taken into account frequently, as, e.g., in the case of medium-size DC drive applications. Based on a suitable normalization, a systematic evaluation of the accuracy of analytical approximations results in corresponding areas of validity depending on the dominant parameter line and DC reactances, respectively, and the effective DC voltage. Thereby, an exact model is proposed to describe the effect of DC ripple on the behavior of harmonic amplitude and phase angle. To predetermine line-current harmonics as easily as possible, the most effective formula can be obtained from corresponding decision areas, whereby the allowable errors are confirmed by comparing results of digital simulation. With the aid of this selection procedure, assessments of worst case situations become feasible. With the knowledge of the phase angles, an estimation of the total harmonic generation of several converters as well as a better judgment of converters attending to preloading supply harmonics are achieved.