DC-DC converters for current flow control, voltage conversion and integration of energy storage systems in DC grids

The advantages of DC transmission over the traditional AC transmission, particularly under medium and high voltage level, are widely recognised in recent years. In order to utilise DC power transmission in a more efficient manner, a construction of multi-terminal DC grids is put forward in previous literature. However, the development of large-scale DC grids faces various technical challenges, such as the power flow management, the voltage conversion and regulation, and the fault current management. One substantial and promising solution against these technical challenges whilst enhancing the controllability and flexibility of DC grids is by the inclusion and control of DC-DC converters. In this thesis, three potential applications of the DC-DC converter in future DC grids are investigated: 1) acting as a DC current/power flow controller for current/power flow management in meshed DC grids; 2) acting as a DC transformer for the interconnection of DC grids; 3) acting as a DC interface for integrating energy storage systems into DC grids.