High-Power DC–DC Converter Utilising Scott transformer Connection

To obtain a resilient and flexible DC grid, reliable means for interfacing its parts operating under different voltage levels must be ensured. This paper proposes bidirectional, isolated, DC–DC converter designed to connect either high/medium voltage bipolar DC grid or two separate high/medium voltage DC grids with another DC grid of similar or different voltage level. In order to achieve galvanic separation among converter stages, while providing redundancy in case of the converter parts malfunction or a DC feeder loss, Scott transformer connection is employed. So far, Scott transformer connection has mostly been used in the railway applications, implying low-frequency operation, in order to obtain two single-phase voltages from a symmetrical three-phase grid. However, its use in the field of the DC–DC conversion has never been analysed in the literature. Further, this paper emphasises operating frequency shift towards the medium frequency range, following the trend of the solid-state transformers which have drawn the attention of both academia and industry worldwide. To control the converter power flow, phase shift control principles are adopted. Consequently, control simplicity is retained, while achieving system complexity reduction. At last, in order to evaluate proposed converter performance, simulation results of a 40 kV/1.5 kV, 10 MW converter are presented, illustrating excellent operating performances.