Modified <i>LLC</i> Resonant Converter With <i>LC</i> Antiresonant Circuit in Parallel Branch for Wide Voltage Range Application
Xiqi Wu, Rui Li, Xu Cai
Abstract
In this article, a modified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> antiresonant circuit in parallel branch is proposed. The proposed converter is derived by placing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> antiresonant circuit on parallel branch. In comparison with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter, the equivalent inductance of parallel branch of the proposed converter decreases along with switching frequency within regulating frequency range. This advantageous property contributes for that the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current and circulating conduction loss in the primary side can be reduced at unity voltage conversion ratio due to large impedance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> antiresonant circuit. Moreover, by optimizing resonant parameters design of parallel branch based on time-domain analysis, the magnetizing current is in close proximity to a sine wave and the conduction loss in the secondary side will be reduced, especially in the light load. A higher voltage conversion ratio can be achieved at low switching frequency due to decreased impedance in parallel branch. In addition, a design flowchart and a design practical case are given to help to implement an efficiency optimization algorithm to decide five resonant design parameters. Finally, a 2 kW 250 V—400 V-input and 48 V-output prototype is built, and the main experimental results are provided to verify the feasibility of the proposed converter and compare with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter. Comparative state-plane trajectories are depicted to compare their characteristics and to verify the model-domain analysis.