PhD student Andrew Stillwell with advisor R. Pilawa-Podgurski
Flying capacitor multi-level (FCML) converters are capacitor-baser power converters that provide high-density and high-efficiency power conversion for dc-dc and dc-ac applications. In many of these applications, there is a need for an auxiliary power supply for control, thermal management, or secondary loads. This auxiliary supply is traditionally sourced from the high-voltage input (which necessitates high voltage and thus large volume) or the output (which creates start-up issues). Due to the multi-level nature of the FCML converter, there exists a naturally occurring, low-voltage node
that enables a compact and highly efficient auxiliary power supply sourced from within the FCML converter, as shown in Figure 21. However, sourcing power from this node disrupts the natural balancing of the flying capacitors, which detrimentally increases the switch voltage rating and the capacitor voltage rating. To compensate for the current sourced to the auxiliary converter, we apply active balancing through feedback and duty-cycle adjustments. This concept was proven with a hardware prototype, shown in Figure 22, and demonstrated excellent flying capacitor balancing. This research is supported by the Army Research Laboratory.