Modified LLC Resonant Converter With LC Antiresonant Circuit in Parallel Branch for Wide Voltage Range Application

In this article, a modified LLC resonant converter with LC antiresonant circuit in parallel branch is proposed. The proposed converter is derived by placing LC antiresonant circuit on parallel branch. In comparison with LLC 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-off current and circulating conduction loss in the primary side can be reduced at unity voltage conversion ratio due to large impedance of LC 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 LLC resonant converter. Comparative state-plane trajectories are depicted to compare their characteristics and to verify the model-domain analysis.