A Scalable Self-Powered Balancing Circuit for High-Step-Down-Ratio Auxiliary Power Supply

This article proposes a new auxiliary power supply solution for medium-voltage converters using a unidirectional-balancing-cell-based approach. The proposed approach reduces the number of active devices and required driving circuitry by half compared with existing voltage-balancing circuit designs. In addition, it significantly reduces the size of the resonant tank by decoupling the
$LC$
resonant frequency from the switching frequency. The proposed solution is scalable and adaptable to different voltage levels. Each balancing cell operates independently in a self-powered manner, enhancing reliability and simplicity. The balancing cells are connected in an interleaved manner, enabling a step-down ratio of
$(n+1):1$
for
$n$
cells. A 6 to
$1 \,\mathrm{kV}$
prototype is presented to verify the proposed concept. To meet the voltage requirement for the auxiliary power in a medium-voltage system, a two-stage high step-down converter was developed. The converter is capable of converting 6 to
$48 \,\mathrm{V}$
and is constructed using the proposed converter as the first stage and commercial power supplies as the second stage.