The use of high voltage dc (HVDC) allows electricity transportation systems to operate with low dc currents and improving efficiency. Interfacing such HVDC systems to the utility grid can be realized using modular multilevel converters. In such a converter, each submodule requires energy from an isolated low power auxiliary supply for the gate-unit. Generally, this is done by means of an external converter since it is not practical to directly step-down the high voltage to required levels. In this context, this work proposes a non-isolated, unidirectional, high step-down voltage-ratio converter based on a stack of buck-boost cells. It is intended as a first stage of a floating auxiliary supply for HVDC submodule gate-units. A 200 W prototype with an input voltage range of 1.5 kV to 3.0 kV and output voltage of 350 V has been implemented.
Gabriel Tibola, TU/e