Improved Light-Load Efficiency Modulation for Wide Voltage Range Single-Stage AC–DC Converter

This article introduces a light-load efficient modulation strategy for single-stage ac-dc converters. The proposed modulation scheme is implemented on a modified push-pull single-stage ac-dc converter. This converter achieves a zero voltage switching (ZVS) turn-on over a wide voltage range at full power with the introduced auxiliary inductor. However, single-stage converters commonly suffer from low efficiency at light loads due to hard switching (HS) and the dominance of circulating current, which causes significant power losses. To address these challenges, this work proposes a modulation strategy that uses adaptive switching frequency to improve light-load efficiency. Experimental results from a 3.7-kW single-stage on-board charger (OBC) prototype are provided to verify the theoretical claims across various load levels. As a result, light-load conversion performance, including efficiency and power quality, is improved. This concept is particularly important for battery energy storage systems (BESSs) and photovoltaic (PV) conversion systems, where diversified load levels are common.