A Modular DC-DC Converter Topology for HVDC Applications

A transformer-less Modular Multilevel DC-DC converter for High Voltage Direct Current (HVDC) applications is proposed in this paper. This topology is suitable for interfacing two HVDC links at different voltage levels using only conventional half bridge submodules. The uniqueness of the proposed converter is in its symmetry in performance in the event of reversal of polarity of one of the DC links. The stable operation of the proposed DC-DC converter is demonstrated by interfacing a voltage sourced converter (VSC) based HVDC with a line commutated converter (LCC) based HVDC. Its bipolar operating capability is shown by reversal of polarity of the LCC based HVDC link. The proposed converter can also be used in the onshore terminal of a platform-less DC collection system for an offshore wind farm and this operation is demonstrated with simulation results. All the necessary simulations for the above configurations are carried out in EMTDC/PSCAD platform.