A Switchable Rectifier-based LLC Resonant Converter for Photovoltaic Applications

Abstract

The conventional LLC converter is popular among the resonant DC-DC converters. However, the switching frequency range limitation affects the operation of the converter under a wider voltage range. The far switching frequency operates away from the resonant frequency; the higher the circulating currents and the lower the overall efficiency are obtained. This paper presents a novel LLC resonant converter with a switchable rectifier that can regulate the photovoltaic panel’s wide low voltage range. The full-bridge circuit on the primary side and a voltage-tripler rectifier, a voltage-fifthfolder rectifier, and a voltage-sixfolder rectifier on the secondary side are employed in a single topology to overcome the disadvantages of the conventional LLC converter. By configuring the rectifier structure and utilizing frequency modulation, the voltage gain is extended with a narrow frequency range around the resonant frequency. In addition, the efficiency is improved, and the size of the transformer is reduced compared to those of the conventional LLC converter. Moreover, zero voltage switching (ZVS) and zero current switching (ZCS) are achieved in all power MOSFETs and power diodes. A 250W converter prototype generating 500 V DC output from a wide-input source was built and tested to verify the proposed converter’s feasibility and effectiveness.