EFFECT OF DC RIPPLE AND COMMUTATION ON THE LINE HARMONICS OF CURRENT-CONTROLLED AC/DC CONVERTERS

Line harmonics are usually predetermined under the simplified assumption that the de current is sufficiently smoothed. However, in practical operation of controlled converters, e.g., feeding medium-size dc drives, it frequently happens that the de ripple cannot be neglected. For the predetermination of line harmonics, this means that the operating point is specified by the emf and the mean value of the dc current, i.e., the associated control and commutation angles, are unknown. The consideration of the basic effects of commutation and dc ripple leads to line current harmonics that are separated into positive and negative sequence systems. Selected results of systematic evaluations show the amplitude and phase as a function of dc reactance as well as of the emf and mean dc current in the range of usual low- and medium-voltage supply networks. In comparison with the conventional precalculation assuming sufficient dc smoothing, significant deviations occur in the case of higher dc ripple.