A Sensitivity-Improved PFM LLC Resonant Full-Bridge DC–DC Converter With LC Antiresonant Circuitry

摘要

An LLC resonant circuit-based full-bridge dc-dc converter with an LC antiresonant tank for improving the performance of pulse frequency modulation (PFM) is proposed in this paper. The proposed resonant dc-dc converter, named as LLC-LC converter, can extend a voltage regulation area below the unity gain with a smaller frequency variation of PFM by the effect of the antiresonant tank. This advantageous property contributes for protecting overcurrent in the case of the short-circuit load condition as well as the start-up interval in the designed band of switching frequency. The circuit topology and operating principle of the proposed converter is described, after which the design procedure of the operating frequency and circuit parameters is presented. The performances on the soft switching and the steady-state PFM characteristics of the LLC-LC converter are evaluated under the open-loop control in experiment of a 2.5-kW prototype, and its actual efficiency is compared with an LLC converter prototype. For revealing the effectiveness of the LLC-LC resonant circuitry, voltages and currents of the series and antiresonant tanks are analyzed, respectively, with state-plane trajectories based on calculation and experiment, whereby the power and energy of each resonant tank are demonstrated. Finally, the feasibility of the proposed converter is evaluated from the practical point of view.