Partial-Power LLC Resonant Converter with Integrated Transformer for Wide Input Range

LLC resonant converters are popular in high-frequency and high-power-density applications with the advantage of excellent soft switching characteristics. Nevertheless, voltage regulation capability is constrained, and additional power losses will be introduced in a wide operating range. A partial-power LLC resonant converter for a wide input range is presented in this article. Two LLC converters are both designed at the open-loop state, performing as a DC transformer (DCX) to realize a constant transformation ratio. System input power is divided into two parts by a series connection of the two DCXs, which is helpful to reduce component ratings. A synchronous Buck-Boost is cascaded with DCX2 to achieve system closed-loop control by pulse width modulation. Most system power is transmitted by DCX1, and a small portion is processed by DCX2, so less power loss will be generated by Buck-Boost. Working principle, parameters optimization, and integration design of magnetic components are introduced in detail in this paper. A 200W 280 V-400 V/48 V experimental prototype with 1-MHz is established to demonstrate the correctness of the theoretical analysis. Peak test efficiency is up to 95.8%, which is improved compared with the conventional two-stage scheme under the same working conditions.