Step-up unidirectional DC-DC autotransformer for HVDC applications

This paper studies a step-up unidirectional DC-DC autotransformer (UUDAT) topology that is dedicated for HVDC application. The UUDAT is composed by series connection of VSC and diode bridges. Because of employing DC-DC autotransformer technology, UUDAT is able to significantly reduce the power ratings of VSC, diode bridges and AC link compared with conventional unidirectional DC-AC-DC technology. Generic controller of UUDAT that enables successful DC power control is designed. DC fault response and DC fault isolation mechanism of UUDAT are analyzed. Cost penalty because of DC fault isolating capability are studied. Technical feasibly of UUDAT is verified by simulations on PSCAD/EMTDC. Results show that the UUDAT is promising to replace conventional step-up unidirectional DC-AC-DC technology under lower and medium DC voltage stepping ratio.