S-parameters characterization and sequence model of three-phase EMI filter

This paper investigates the characterization of three-phase EMI filter using S-parameters and the use of sequence model to fully describe the high frequency behavior. Characterization of three-phase EMI filter helps to understand the influence of real filter on overall EMI performance and provides information for filter selection or design. The characterization is divided into two types: component level or system level, which can be chosen to use according to design conditions. S-parameters are chosen as network parameters to characterize because of the convenience to measure them in high frequency range. Beside circuitry model of filter, sequence model of filter is proposed to better describe the attenuation and conversion between different forms of noise, which improves the understanding towards filter behavior compared to traditional separation of common and differential mode noise. Corresponding equations are provided to obtain parameters in the sequence model. At the end, the predictions of insertion loss and energy transfer ratio which represent the grade of mode conversion based on sequence model are shown and compared with results from conventional measurement method.