Generalized Differential-Common-Mode Decomposition for Modeling Conducted Emissions in Asymmetric Power Electronic Systems

This paper proposes a generalized approach to decompose mixed-mode (MM) conducted emissions in power electronic systems into their differential and common-mode components and modal couplings. Specifically, a pair of transformation matrices are defined that map a system of MM line-to-ground voltage equations to an equivalent decomposed differential-common-mode set. The result provides exact mathematical relationships for the modal couplings induced by asymmetries between the lines described by the voltage equations. As an example, the proposed transformation is applied to generate two different, but equally valid models for studying the effect of unbalanced parasitic capacitances in a multichip power module on the common-mode (CM) behavior of a half-bridge converter. The two models provide different perspectives on the mechanisms driving CM current through the system. It is found that one model is best suited to study leakage current through the module while the other provides greater insight into currents circulating internally and its impact on the larger system.