Switched-Capacitor LLC Resonant DC-DC Converter with Switch Peak Voltage of Vin/2

Abstract

A DC-DC hybrid switched-capacitor LLC resonant converter integrating a ladder cell at the input of the LLC resonant converter using frequency modulation is proposed in this paper. This converter has six switches that are subjected to half the voltage of the input source. All switches commutate at zero voltage over the entire load range, and the diodes of the output rectifier bridge commutate at zero current. The proposed converter has the following characteristics: (a) symmetrical operation, (b) simple frequency modulation, (c) commutation of all switches at zero voltage, (d) all switches subjected to half the input voltage, and (e) static gain practically immune to load variations. Theoretical analysis, design, and experimental results in the laboratory for a prototype of 2 kW, 1000 VDC input, 48 VDC output, and 90 kHz switching frequency are included in this study. The maximum efficiency measured was 97.3%.