A High Step-up Modular DC/DC Converter for Photovoltaic Generation Integrated into DC Grids

A high step-up-ratio DC/DC converter for photovoltaic energy integrated into high voltage DC grids is proposed in this paper. The converter is mainly composed of modular DC/DC conversion modules which are configured as input-parallel-output-series structure. The proposed module is consisted of two power stages, with a boost circuit as the first stage and a narrow-switching-frequency-variation LLC circuit as the second stage. The interleaved technique of the boost stage effectively reduces the input and output ripples without adding extra components. Full-range soft-switching property is achieved to the LLC stage to minimize switching losses. Theoretical analysis is carried out for the system voltage gain and design principle of the LLC resonant tank. The simulation and experimental results of a 3kW prototype circuit is presented to verify the theoretical analysis and principles for the proposed module.