A 500 kHz Wide Output LLC-T Resonant Converter With Narrow Frequency Range, Reduced Circulating Energy, and Low Voltage Stress

The resonant converters are promising topologies for the electric vehicle charging applications due to the soft switching feature. However, the conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter regulates the wide output voltage through a wide frequency range, which leads to low efficiency with large circulating energy and the difficulty of the resonant tank optimization. This article proposes a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i>-T resonant converter, which parallels an auxiliary transformer with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonant tank for the wide output applications. The proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i>-T resonant converter narrows the frequency range with less circulating energy, lower voltage stress on the resonant capacitor, and smaller flux linkage in the resonant inductor compared to the conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter. Meanwhile, the zero-voltage switching turn-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> is maintained throughout the wide output voltage range and load range. Furthermore, a precise time-domain based analysis and the design methodology are proposed. A 500-kHz, 1.35 kW, 400 V input /250 V–450 V output prototype is built to verify the concepts of the proposed topology and demonstrates a 97.82% peak efficiency.