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, the 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. The two LLC converters are both designed at the open-loop state, performing as a DC transformer (DCX) to realize a constant transformation ratio. The system input power is divided into two parts by the series connection of the two DCXs, which is helpful to reduce the components ratings. A synchronous Buck-Boost is cascaded with DCX2 to achieve the system closed-loop control by pulse width modulation. Most of the system power is transmitted by DCX1 and a small portion is processed by DCX2, so less power loss will be generated by Buck-Boost. The working principle, parameters optimization and integration design of magnetic components are introduced in detail in this paper. A 200W 280V-400V/48V experimental prototype with 1-MHz is established to demonstrate the correctness of the theoretical analysis. The peak test efficiency is up to 95.8%, which is improved compared with the conventional two-stage scheme under the same working conditions.