A Scalable Voltage-Balancing-Circuit based Non-Isolated High-Step-Down-Ratio Auxiliary Power Supply

This paper proposes a non-isolated high-step-down-ratio auxiliary power supply solution for medium-voltage converter. Different from the state-of-the-art voltage-balancing-circuit designs, the proposed unidirectional balancing cell can reduce a half of the active device and their driving circuits. Also, size of the resonant tank can be shrunk by more than ten folds by decoupling the LC resonant frequency from the switching frequency. Lastly, the balancing cells are connected in an interleaved manner instead of direct series connection. In this way, each balancing cell is self-governed and decoupled from other cells, which eliminates the need for communication or central controller, and improves both reliability and simplicity. The solution, therefore, becomes a scalable and flexible solution for different voltage levels. For n cells, when stacked in an interleaved way, the topology can have n times of input voltage, and (n+1) : 1 step-down ratio. Finally, a 100 W prototype that converts 6 kV to 1 kV using five cells with different power flow directions validates the working principle.