A Hybrid Half-bridge LLC Resonant Converter and Phase Shifted Full-bridge Converter for High Step-up Application

Abstract

High step-up DC/DC converters are popular in renewable energy generation systems, like photovoltaic (PV) and fuel cell. To achieve high step-up conversion ratio, in this paper, an input-parallel and output-series hybrid topology of half-bridge LLC resonant converter and phase shifted full-bridge converter (PSFB) is proposed. The following features have been achieved: 1) high voltage conversion ratio: due to the output series connection, the system voltage conversion ratio equals to the sum of LLC resonant converter and PSFB converter. In addition, the voltage doubler rectifier is adopted for the LLC resonant converter to further increase the voltage gain; 2) LLC resonant converter is operating at the series resonant frequency operating point, its voltage conversion ratio is constant and independent of the load, and the high efficiency conversion is achieved; 3) function decoupling idea is adopted for the proposed topology, most of the power is handled by the high efficiency conversion unit-LLC resonant converter, while the PSFB unit is used to regulate the output voltage; 4) since both two converter units are isolated DC/DC converter, fully isolation between the input voltage and output voltage is achieved. Operational principles, design considerations, and experimental validation are presented.