An Integrated S ⁴ Buck‐Boost‐LLC AC‐DC Converter for High‐Efficiency, Cost‐Effective LEV Charging Applications

ABSTRACT Single‐stage AC‐DC converters are highly suitable for light electric vehicle (LEV) charging applications due to their high efficiency and low cost. However, conventional single‐stage Boost and Buck‐Boost AC‐DC converters often face challenges such as high or wide bus voltage, narrow load operation range, and increased cost. To address these issues, this paper proposes a novel integrated single‐stage soft‐switching (S 4 ) Buck‐Boost‐LLC AC‐DC converter. By controlling the main switch on the Buck side of the Buck‐Boost power factor correction (PFC) cell, a low and narrow bus voltage is achieved under universal input conditions. Furthermore, an optimal design methodology and a simple single‐feedback loop control strategy are developed to ensure full‐load range operation. Notably, the LLC resonant cell functions as a DCX converter under high‐input voltage or light‐load conditions. A prototype with an input voltage range of 85 to 265 V and an output of 12 V/25A is constructed to validate the proposed solution. Experimental results demonstrate that the prototype achieves a bus voltage range of 260 to 360 V, a peak efficiency of 91.6% across the entire input voltage and load range, and the measured power factors are above 0.983 at full‐load condition.