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 1kV 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 48V and is constructed using the proposed converter as the first stage and commercial power supplies as the second stage.