A Novel Soft-Switched Single-Stage AC/DC Converter Integrated BCM PFC and Nonresonant DC–DC Cell With High PFC Performance and Wide Load Operation Range

Abstract

The traditional boost-LLCsingle-stage ac/dc converter has been attractive because of its soft switching feature and simple structure. Unfortunately, high and significantly varying bus voltage, as well as narrow load range greatly hinder its application at high voltage input. Therefore, this article proposes a novel soft-switched single-stage ac/dc converter for high voltage input applications. Aiming at the high bus voltage issue, a boost power factor correction (PFC) cell with inherent boundary conduction mode operation is adopted. Meanwhile, a nonresonant half-bridge dc/dc is incorporated to make the power transmission characteristics of the PFC and dc/dc cells more consistent. As a result, the proposed converter can achieve a broader load range and quasi-constant bus voltage compared to the previous approaches. Furthermore, an improved pulse frequency modulation (PFM) control is put forward so that the PFC performance under high inputs can be greatly enhanced. To validate the claimed features, a 104 W prototype was built in the laboratory, operating with an input range of 180 to 260 V and an output voltage of 52 V. Experimental results show that the following. 1) Low and quasi-constant bus voltage during the operation ranges is achieved. 2) Under PFM control, a broader load range across entire inputs is realized, ranging from 30%–100%. 3) The prototype exhibited good overall performance, achieving a peak efficiency of 93.8% and a nominal efficiency of 93.3% at full load. Meanwhile, the measured nominal power factor (PF) and minimum PF under full load conditions reached 0.991 and 0.987, respectively.