The Cascaded Resonant Converter: A Hybrid Switched-Capacitor Topology With High Power Density and Efficiency

Resonant switched-capacitor (ReSC) converters have efficient utilization of both active and passive components, and hold the potential to achieve higher efficiency and higher power density than conventional switched-capacitor (SC) and magnetic-based converters. This article presents a new hybrid/resonant SC converter topology, comprising two cascaded 2-to-1 ReSC converters, to address high-conversion-ratio applications. The proposed cascaded resonant converter has a simple structure and operation principle and can achieve one of the best overall metrics among popular ReSC topologies. A 36-60-V input 4:1-fixed-ratio bus converter prototype for data center application is designed and constructed. We present detailed design guidelines and discussions to address practical challenges, such as component variations and interstage decoupling requirements. With 48-V input and operating at the typical zero-current switching mode of ReSC converters, the prototype achieves a peak efficiency of 98.85% (including gate drive loss) and a power density of 2500 W/in
³
, both of which are significantly higher than the state of the art. Furthermore, we propose a zero-voltage switching method to improve light-load efficiency. Through this control method, which greatly reduces the output capacitance loss, the prototype can maintain an efficiency above 97% starting from 3% of the rated load, with a peak of 99.0%.