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 for different purposes: (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 1 MHz, 24 V-to-3.3 V, 5.5 W active-clamp LLC module prototype. The performance of PI and PID system controllers is analyzed and compared by simulations of a twenty-module system.