Unity power factor three-phase AC-DC converter applying two switch DCM SEPIC converter with coupled inductors

A two switch three-phase power factor correction SEPIC converter with coupled inductor operating in discontinuous current mode is presented. The switches voltage stress in this converter is related to peak of phase voltage instead of line voltage. Also, applying coupled inductor technique, not only reduces number of the magnetic cores but also with suitable design of coupling coefficient, input current ripple cancellation is achieved, so smaller inductor size can be used as input inductance. Thus, the proposed converter only applies three magnetic cores and <5% THD is achieved with the proposed converter in a wide range of load and input voltage variations. Input phases are decoupled so converter can keep unity power factor even under unbalanced input source. Operating modes of the proposed converter is explained, and its input impedance is determined. It is verified that input impedance is pure resistive. The mathematical analysis and design procedure are discussed. Design example and experimental results from 400W prototype with 220V line to natural input RMS phase voltage and with 400V output voltage operating at 40kHz are presented to verify theoretical analysis.