DCM and CCM Operation of Buck-Boost Full-Bridge DC-DC Converter

Buck-Boost based full-bridge DC-DC converters possess potentials for high gain, high power applications, particularly in solar PV, battery, and fuel-cell fed systems, as the converters feature non-pulsating input and output currents. However, these converters lack attention due to the presence of DC-current in the transformer winding. In this paper, a novel Buck-Boost full-bridge (BBFB) converter with a hybrid control scheme (HCS) mitigating the transformer DC-current is presented. The BBFB converter exhibits inherent soft-switching such that zero voltage switching (ZVS) conditions apply for individual switches. This paper analyzes the BBFB converter extensively, including the discontinuous conduction mode (DCM) operation and the DCM boundary condition. A dynamic behavior of the BBFB converter under a load step change verifies that the HCS scheme does not affect the converter performance. Besides, this work presents a model for the high frequency oscillations that occur in the practical transformer current waveform due to parasitic capacitances. All the analyses and the developed models are verified in simulations and hardware experiments. The developed models are useful for designing the BBFB converter with improved efficiency by ensuring the ZVS operation. Further, the developed models and results provide an insight for the DC voltage gain variations during DCM and continuous conduction mode (CCM). This helps the designer to choose the BBFB converter's operating mode based on the requirement.