High‐power DC–DC converter utilising Scott transformer connection

Abstract

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 solidstate 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.

Swiss competence center on energy research FURIES - Overview and contributions in the area of power electronics and SmartGrids

“…The STC, achieved by appropriate connection of two single-phase transformers, allows for creation of balanced three-phase voltage from set of in-quadrature single-phase, or vice versa. For those reasons, two MMC-based single-phase converters are connected to the STC on the high voltage side, while simple [3]. Important characteristic of the topology from Fig.…”

“…1 (b), is the ability to provide fault tolerant operation in case of loss of one pole in the MVDC grid (in case of bipolar network). Ability to perform in this operating mode has some implications to the converter sizing, as discussed in [3], but this is beyond the scope of this paper.…”

State diagnosis method of transformer winding deformation based on fusing vibration and reactance parameters

“…The transformer is one of the most crucial transformation and transmission equipment, which plays a key role in connecting power grid of different voltage levels. The security and reliability of the power system are closely related to the stable operation of transformers [1]. Therefore, status monitoring and fault diagnosis on transformers become research hotspots in the industry [2][3][4][5].…”

Soft‐switching and sensorless voltage balancing modulation for unidirectional modular multilevel DC–DC converter

“…When the MVDC distribution network is connected to LVDC loads such as industrial facilities, data centres and electrical vehicle (EV) charging stations, galvanic isolation is mandatory [4, 6–8]. In such scenarios, multilevel structures should be utilised on the MVDC side to handle the high voltage, and uncontrolled rectifiers could be used on the LVDC side for cost‐efficient purposes, and a transformer is applied as the AC link for galvanic isolation [8, 9].…”