A family of un-isolated modular DC/DC converters

A family of un-isolated modular dc/dc converters (MDCC) are presented by replacing the complementary switches in classical dc/dc converters (buck, boost, cuk, etc) with 2 chains of submodules (abbreviated as complementary chain-links) and an inductor. A stepped 2-level operating mode of chain-links is proposed to achieve the voltage balance of the submodule capacitors. A buck type modular multilevel converter (Buck-MDCC) derived from buck converter is presented to illustrate the operation principle. The proposed converters are suitable for high voltage dc conversion due to the voltage press of submodule switches can be dramatically reduced by cascading more submodules. Moreover, the dν/dt of the converters can be controlled with stepped 2-level modulation. The proposed converter also offers the merits of lower ac circulating current and lower submodule capacitance requirement compared with prior arts of MDCCs, where the sine-wave modulation is adopted.