Multi-cell DC-DC converter with high step-down voltage ratio

The use of high voltage allows a power processing system to operate with low currents, improving efficiency. Nevertheless, final applications usually require low voltage inlet, which can be provided using modular multilevel converters submodules, for instance. However, every submodule's gate-unit requires energy from an isolated low power auxiliary supply. Generally, this is done by using an external converter since it is not practical to directly step-down the high voltage to required levels. In this context, this paper proposes a multi-cell solution based on stacking of buck-boost converters intended to be the first non-isolated stage of an isolated high step-down voltage ratio converter. Analysis and design are presented together with experimental verification of a 200 W rated power converter with 1.5 kV to 3.0 kV input voltage range and a nominal output voltage of 350 V.