Geometrical State-Plane Analysis of Resonant Switched-Capacitor Converters: Demonstration on the Cascaded Multiresonant Converter

Abstract

To realize high efficiency and high power density for resonant switched capacitor (ReSC) converters, it is critical to have a thorough understanding of the soft-switching mechanism and design the converter appropriately. However, this can be challenging as the soft-switching operation depends on multiple variables and its design difficulty increases quickly with respect to the topology complexity. This paper demonstrates a framework of using geometrical state-plane analysis to facilitate ReSC converter design. The methodology is first applied to a basic 2-to-1 ReSC converter, and then extended to a new 4-to-1 ReSC converter topology we proposed, herein named cascaded multi-resonant converter. This topology has reduced component count thanks to a new "switching bus" architecture. However, it comes at a cost as the converter has multiple resonances within each switching cycle, complicating the soft-switching design. Despite the high circuit complexity, the state-plane analysis neatly provides analytical equations of all state parameters, which are verified by simulations and experiments. Our hardware prototype achieves 6000 W/in 3 power density at 48-to-12 V conversion and 80 A continuous output. Its peak efficiency reaches 99.02%, and full-load efficiency reaches 97.67%, including gate drive loss. Both the power density and efficiency are superior to the state-of-the-art 48-to-12 V solutions.

The Switching Bus Converter: A High-Performance 48-V-to-1-V Architecture With Increased Switched-Capacitor Conversion Ratio

“…Other switching-bus-based regulated hybrid SC topologies include the MLB converter [20] and the CaSP converter [17], with all benefiting from a similar reduction in switch count due to the strategic merging of adjacent stages. In addition, the switching bus concept can also be employed to construct fixed-ratio multi-resonant SC topologies [35] for intermediate bus converters (IBCs) in data center applications.…”

“…As an emerging family of topologies, hybrid SC converters have received increased attention, since they can leverage both the greatly superior energy density of capacitors compared to magnetics [30], [31] and the better figure-of-merit (FOM) of low-voltage switching devices compared to highvoltage devices [32]. To date, resonant switched-capacitor (ReSC) converters have also demonstrated superior performance to transformer-based converters for non-isolated fixedratio power conversions in data center applications [33]- [35].…”