A Transformerless High-Voltage DC-DC Converter for DC Grid Interconnection

This paper presents a transformerless high-voltage dc-dc converter based on cascaded sub-modules. It is intended for interconnecting high-voltage or medium-voltage dc grids. The proposed dc-dc converter consists of two phase legs, each of which consists of an upper arm and a lower arm with their middle nodes crossly connected through a branch of active sub-modules. By properly controlling the output voltage of the cross-connected branch, a trapezoidal ac current is induced to interact with the ac voltage components in the upper and lower arm for rebalancing the power amongst converter arms. The features of modular design, single-stage power conversion, and transformerless structure make the proposed dc-dc converter gain the outstanding merits of wide voltage ratio range, high system efficiency, and light converter weight. A control scheme is also elaborated for guaranteeing the normal operation of the proposed dc-dc converter. A 100-kV 100-MW simulation model performed in MATLAB/Simulink verifies the feasibility of the proposed dc-dc converter. Experimental results obtained from a 100-V 1-kW laboratory setup also confirm the validation of the proposal.