A High-Power-Density High-Efficiency Soft-Switched Single-Phase Universal Input to 28-V Isolated AC–DC Converter Module Designed for Paralleled Operation

Abstract

This article presents a high-power-density high-efficiency soft-switched single-phase universal input to 28-V isolated ac–dc converter module designed for parallel operation. The proposed two-stage converter utilizes a totem-pole bridgeless boost power factor correction (PFC) ac–dc converter stage followed by an isolated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant dc–dc converter stage. A comprehensive design and optimization methodology is presented that compares various designs and operating modes for the converter's power stages and selects the optimal design based on overall power density and efficiency. Additionally, a control scheme is presented for the PFC stage to minimize current distortion by accounting for various sensor, control, and gate-drive delays while ensuring zero-voltage switching (ZVS) of the transistors. Moreover, a new droop control strategy is presented, which utilizes the input current of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> dc–dc stage to ensure equal output current distribution between paralleled modules powering a common output load. To validate the proposed design and control strategy, two 1-kW universal input to 28-V isolated ac–dc converter modules are built and tested. Each prototype converter module achieves a high power density of 84 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a peak efficiency of greater than 93% while ensuring a current distribution error of less than 0.3% when operating in parallel to deliver the maximum output power of 2kW.