ON/OFF Control of a Modular DC–DC Converter Based on Active-Clamp LLC Modules

This paper studies ON/OFF control of a dc-dc system that contains multiple active-clamp LLC resonant modules operating in parallel. The architecture and the ON/OFF control method yield high overall efficiency and fast transient responses. Two converter models are introduced: 1) a high-frequency model to determine a gate timing sequence that enables fast ON/OFF control, and 2) an averaged model to assist in the system control loop design. The models and the ON/OFF control method are verified by experiments on a prototype consisting of two 1-MHz, 24-3.3-V, 5-W active-clamp LLC modules. The performance of PI and PID system controllers is compared, and capacitor size is analyzed by simulations on systems containing up to 20 modules.