A Three-Phase Off-Line Switching Power Supply with Unity Power Factor and Low TIF

A new three-phase off-line switching AC/DC converter is described, one which draws essentially sinusoidal AC currents from the input line and therefore generates a very low TIF (Telephone Influence Factor) in the three-phase line currents. The converter consists of three two-stage power processors, the first stage of each performing the unity power factor conversion and the second stage providing isolation and combining the power to a single DC output. The converter easily can be reconfigured to operate from either a single-phase or three-phase (wye or delta) input line. In addition to providing the benefits of unity power factor operation (i.e., good power utilization of source volt-ampere capacity, negligible harmonic currents and low TIF), the converter can operate from a wide range of input voltages because it minimizes voltage stresses to which power switches are exposed. The power stages and control circuits used in a 2 KW implementation of the converter are described and modeled. Some measurements demonstrating the operation of the converter are presented.