Modeling of AC/DC converters under unbalanced voltage supply using complex switching functions

To investigate harmonics in AC/DC converters under unbalanced voltage supply, an improved modeling using complex switching functions is proposed. A consequent formulation by positive and negative sequent systems allows a unique and compact representation of switching functions, if the negative axis is introduced for negative sequent components. Thus, simplified evaluations and a better physical understanding of the generation mechanisms of nonregular harmonics is achieved. Furthermore, the effect of DC current ripple on control and overlap angles is described approximately based on linearized time discrete models. This results into a significantly higher accuracy of evaluation compared with conventional good DC smoothing assumption. Selected examples show the efficiency of the proposed method.