Modeling of AC/DC Converters Under Unbalanced Voltage Supply Using Complex Switching Functions

摘要

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 non-regular 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.