A LLC resonant converter with a notch filter at secondary side for high step-up and wide voltage range applications

A multi-resonant converter is proposed by embedding a notch filter at secondary side in the conventional LLC converter for both high step-up and wide voltage range applications. Compared to LLC converter, the proposed converter can achieve wide voltage regulation within relatively narrow switching frequency range, and also the proposed resonant tank can effectively transfer both fundamental and third harmonics elements, resulting in high conversion efficiency. By moving the LC notch filter of the LCLCL converter to the secondary side, the proposed converter avoids the circulating currents at primary side flowing through LC notch filter, which benefits to reducing conduction losses. The operation principles and characteristics are analyzed in detail using first harmonic approximation. A 400W prototype with input voltage range from 25V to 50V was built, and experimental results show overall efficiency of the proposed converter is 1.5% higher than LCLCL converter, which indicates the feasibility of the proposed converter in high step-up and wide voltage range applications.