Analysis and design of a series-resonant NPC dc-dc converter for auxiliary supply applications in dc grids

Dc-dc converters in dc grids fulfill a similar function as ac transformers in ac grids. Contrary to an ac transformer, a dc-dc converter requires an auxiliary power supply for operation. This paper presents an auxiliary power supply that provides a galvanically isolated low voltage dc output from a medium-voltage dc input. The employed series-resonant Neutral-Point-Clamped (NPC) topology and its modulation scheme are introduced and analyzed. Furthermore, a transformer with high voltage-ratio and low stray capacitance is presented and isolating gate drivers are described. Simulations including the parasitic effects of the components are performed. The converter is implemented and tested. Measurements verify the previous analysis and simulations.