Input voltage feed-forward control strategy for cascaded DC/DC converters with wide input voltage range

LLC resonant converter can implement Zero-Voltage-Switching (ZVS) in full load range through appropriately designing transformer's magnetic inductance, leakage inductance and circuit's quality factor. This kind of LLC resonant converter always runs in a nearly constant voltage gain no matter how the load changes. Thus it can be unregulated. By introducing an input stage converter which implements regulating output voltage, the converter can be optimally designed and high efficiency can be accomplished. But as the existence of a zero in right-hand half plane of Boost converter and the beat frequency characteristic of LLC converter, conventional Proportional-Integral (PI) controller can't meet the fast response requirement. This paper deduces a simplified expression of transfer function from control to output voltage and designs a lead compensator on the basis of PI controller. At the same time, an input voltage feed-forward control strategy is proposed to reduce output voltage variation when input voltage changes dramatically. Experimental results verify the effectiveness of the proposed control method.