Proposal and analysis of three-phase filter by using mixed-mode S-parameter based on Fortescue transformation

In this paper, we propose a new method for evaluation of a three-phase filter, utilizing a “mixed-mode S-parameter based on Fortescue transformation.” Because the positive phase sequence is the main component of current in a three-phase circuit, it is necessary to be able to analyze this response. Moreover, it is important to assess the effects of the zero phase sequence in order to investigate both conductive and radiative noise. To perform these analyses, it is useful to transform voltage and current into symmetrical coordinates, which leads to the mixed-mode S-parameter. Measurement examples based on this method are given in this paper. Because three-phase filters with cyclic symmetry have zero matrices as off-diagonal blocks in the mixed-mode S-matrix, each phase sequence becomes independent and non-interactive. Accordingly, by using the multi-section theorem, we can decompose the filter into modal equivalent circuits; the results calculated with these circuits agree well with those obtained from the measurement.