A modular DC/DC photovoltic generation system for HVDC grid connection

A modular DC/DC conversion system with distributed MPPT and centralized step-up converter for photovoltaic energy integrated into HVDC grids is proposed in this paper. The conversion system consists of two power stages, with MPPT converter as the first stage and a step-up converter as the second stage. Both stages are modular structures. For the distributed MPPT stage, interleaved boost topology is utilized to effectively reduce the input and output ripples without adding extra components. For the centralized step-up stage, narrow-switching-frequency-variation LLC topology is employed, with the modules being configured as input-parallel-output-series structure. Full-range soft-switching property is achieved in the LLC stage to minimize switching losses. Theoretical analysis is carried out for the system voltage gain and design principles. Simulation and experimental results of a 3kW prototype system are presented to verify the theoretical analysis of the proposed system.