Performance analysis of input voltage auto-balanced LLC converter with resonant switched capacitor

Abstract

An advanced LLC series resonant converter (SRC) with resonant switched-capacitor technique is proposed in this paper to satisfy the high voltage and high step-down requirements. The series structure in the high-voltage side, together with a switched capacitor and its resonant inductor, effectively reduces the voltage stress on the high-side switches to half of the input voltage, which enhances the capability of handling high voltage. Furthermore, high DC voltage step-down conversion is achieved through the combination of the resonant switched capacitor technique and the LLC resonant technique. All the main switches in the proposed converter can achieve zero voltage switch (ZVS) turn-on performance and all the rectifier diodes can achieve zero current switch (ZCS) turn-off performance from no load to full load with wide-input-voltage range. Besides, the conduction loss of the power switches is reduced by half, which can further improve the efficiency of the converter. Finally, a 500V~640V-input 48V-output 900W prototype is designed and built to verify the effectiveness of the proposed converter. The results have proved that the proposed converter is an excellent solution for high efficiency, high power density, high voltage and high step-down conversion.