Capacitor-Clamped LLC Resonant Converter Operating in Capacitive Region for High-Power-Density EV Charger

Abstract

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is one of the most commonly adopted topologies for electric vehicle (EV) battery charging. However, due to the wide variation range of battery voltages, applying conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters usually results in relatively larger magnetic size and lower power density. This article presents a novel approach to improve the power density performance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters for EV charging. It leverages the existing capacitor-clamped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> topology, which was originally proposed for applications needing overcurrent protection, while innovatively operating the converter in the capacitive (rather than inductive) region of conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters. Results in this work using our proposed design method show that when working in the capacitive region, the capacitor-clamped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter can not only realize zero-voltage switching in the MOSFETs and zero-current switching in the output diodes but also significantly reduce the flux linkage requirement in the transformer compared to conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> . This leads to an elegant solution that optimally minimizes the size of magnetics for increased power density while reducing costs. The merits of the capacitor-clamped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter with the proposed design method are validated by a 400 W, 200 V input, 125–210 V output range prototype, which achieves an efficiency of 98.13% at the maximum output power.