Modal Theory and Approach for Accurate Characterization of Common-Mode Chokes

This article presents a method for characterization of common-mode chokes aimed at constructing accurate virtual prototypes of electromagnetic interference filters. This method is based on a general modal analysis that identifies the natural modes of a symmetric four-port network in a power line. Natural modes excited in the setups defined in the CISPR-17 norm to characterize filtering devices are determined. From this analysis, two simple measurement setups particularly suitable for characterizing common-mode chokes are identified, and a decision-making algorithm is presented to determine the parameters of a configurable circuit model of the common-mode choke. This circuit model is especially devised so that each one of its different circuit blocks can be associated with a single modal response of the common-mode choke. This, along with the use of physical criteria to define the basic schematic of each circuit block, ensures the simplicity, accuracy, and generality of the final circuit model. Characterization of many commercial common-mode chokes with different core materials and winding configurations has been carried out to demonstrate that this circuit model is able to accurately account for the actual response of different types of common-mode chokes in a wide frequency range.