Aggregated modeling and control of integrated boost-flyback high step-up converter

Integrated boost-flyback converter (IBFC) is constructed with the cascade connection of a boost converter and a flyback converter, it has the advantages of high step-up output voltage and system isolation. Since the boost converter and flyback converter operate in different conduction mode while sharing main switch and dc-link capacitor, a theoretical modeling approach and mathematical procedure are complex when the circuit analysis of two converters are attempted simultaneously. Therefore, this paper proposes the aggregated approach to model the IBFC for understanding of its dynamic characteristic. The basic concept of the aggregated modeling is to substitute the boost or the flyback converter with an equivalent current source, and then to derive dynamic equations for the separated converters by state-space average technique. The proposed approach is simplified intuitive circuit analysis. Furthermore, relevant controller is designed based on the achieved control-to-output transfer function. The frequency response taken from a 100W IBFC and dynamic response taken from the 200W prototype interleaving two 100W IBFC show a good agreement with the theoretical expectations.