Input Voltage Auto-balanced LLC Converter With Resonant Switched-Capacitor Technique

High voltage DC/DC converters have been widely employed in the three-phase communication power supply systems, DC transmission for large offshore wind farm and DC distribution as the interface between the DC transmission and distribution system or energy storage components. However, high input voltage and high step-down DC/DC converters are still challenging in the power electronics community due to the technological limitations of semiconductors with high blocking voltage.An advanced hybrid LLC series resonant converter with integrated flying-capacitor cell is proposed in this paper to enable the high step-down conversion in the high input voltage applications. The inherent flying-capacitor branch in the primary side can effectively halve the primary switch voltage stress compared with the half-bridge LLC converters. Moreover, the inherent soft switching performance during wide load range that exists in the LLC converters is still kept to reduce the switching losses, which ensures the high efficiency. Besides, wide-range voltage regulation is achieved due to the frequency-gain characteristics of the LLC resonant tank.Finally, a 500V～640V-input 48V -output 1kW prototype is built and tested to verify the effectiveness of the proposed converter. The results prove that the proposed converter is an excellent candidate for the high input voltage and high step-down DC/DC conversion systems.