A Dual-Transformer-Based LLC Resonant Converter With Ultrawide Output Voltage Range

This article proposes a novel dual-transformer-based LLC resonant converter with ultrawide output voltage range. The proposed converter utilizes five mosfets and four diodes to combine four operation modes, achieving a 7.5 times ultrawide output voltage range within a squeezed switching frequency range. Zero-voltage switching of all mosfets are achieved as well. A new simplified time-domain analysis methodology is employed, which considers the influence of the output load and dc blocking capacitors, offering high accuracy and small computational requirements. Then, a partial parameter asymmetric design method is proposed, effectively reducing the voltage gain margins between adjacent modes and simplifying the design process. In addition, a new pulse-frequency modulation plus pulsewidth modulation hybrid control strategy is proposed, which fully considers the influence of dc blocking capacitors charging and discharging, achieving smooth, and fast mode transitions. To verify the feasibility of the proposed converter, a 900 W experimental prototype with 380 V input and 60 – 450 V output is built and tested.