Design of an Indirectly Coupled Filter Building Block for Modular Interleaved AC–DC Converters

This article presents the analysis and realization of a modular interconnected filter building block (FBB) operating under a single and multichannel (parallel three-phase converter blocks) configuration without loss of attenuation to any harmonic components. Emphasis is on the design of coupled inductor (CI) and boost inductor. In order to achieve a modular scheme with interleaved operation, indirect coupling between converters is realized using the secondary loop (SL)-based interconnection with inserted impedance. Here the “SL” serves as an additional pass for average grid side currents for N channels. A building block type configuration has been proposed using this topology, inspired by the power electronics building block (PEBB) nature. The purpose of the loop is to interconnect the parallel converters in series using an arrangement of CIs. In addition, a boost inductor has been introduced in the SL to realize a power factor correction rectifier operation. The CI serves as the circulating current filter while reflecting channel currents toward the SL. To meet conducted electromagnetic interference (EMI) limits, a two-stage LCLC filter has been integrated with the FBB by introducing the point of common coupling (PCC) connection between two stages for filter size reduction. A design procedure is presented to meet power quality, circulating current, and EMI limits as per industry standards (EN-55011 and IEEE-519/1594). The proposed FBB has been characterized using 3L-NPC converters enabled with 1.2 kV Silicon Carbide based modules with comprehensive performance validation up to three channels in parallel with 15-kW power rating per channel.