A Boost and LLC Resonant–based Three-port DC–DC Converter

A new three-port LLC resonant converter interfacing an input port, storage port, and load for a photovoltaic (PV) microinverter with high-DC bus applications is proposed. Pulse frequency modulation and pulse width modulation are adopted to regulate the power flows. On the primary side, two switches are implemented to reduce the switch count. On the secondary side, a voltage quadruple rectifier and voltage fifthfolder rectifier are employed in one structure to make the proposed converter operate close to and below the resonant frequency and to boost the voltage with a moderate transformer. The proposed converter can achieve soft-switching for MOSFETs and all rectifier diodes. Moreover, improved efficiency and narrow switching-frequency range are realized. A 300-W laboratory prototype generating 500 V from a wide voltage range of PV and battery is built and tested to verify the theoretical analysis and performance of the proposed converter.