Am Dienstag den 16. April setzt sich das IHT-Kolloquium fort, es spricht:
Frau Stefanie Heinig
Department of Electric Power & Energy Systems,
School of Electrical Engineering,
KTH Royal Institute of Technology, Schweden
„Modular Multilevel Converters for Future Meshed High-Voltage Direct Current Grids”
This Ph.D. project addresses the need to investigate new submodule (SM) topologies for modular multilevel converters (MMC) with extended functionality which can be applied in future demanding applications such as meshed high-voltage direct current (HVDC) grids.
Supergrids based on HVDC technology are foreseen to be the most attractive solution for handling of massive power variations in electricity grids where most of the generated power originates from renewable power sources. As the direction of power in such grids may change on many of the interconnections voltage source converters (VSCs) are preferable. The state-of-the-art VSC for HVDC transmission is the MMC. When planning HVDC grids with MMCs, one of the most important aspects to consider is DC side fault handling. Even if HVDC circuit breakers have been proposed, cost savings are highly probable if the DC side fault current can be controlled by the converter itself and ancillary services can be provided to the connected AC power system during fault conditions.
One promising approach to find advanced SM topologies is based on the idea to equip SMs with more than one capacitor each. This approach leads to improved SM topologies with essentially reduced power losses, such as the semi-full-bridge (SFB) or the double-connection of the novel Double-Zero-Submodule (DZ-SM). Both topologies enable efficient handling of DC side short circuits, whereas the SFB also uses less semiconductors than two conventional full-bridge (FB) SMs. Both SMs provide the possibility to operate the converter at increased modulation indices which can significantly reduce the energy storage requirements of the submodule capacitors. Many aspects of the SFB and the DZ-SM topologies have not been investigated extensively. Moreover, the application of advanced silicon carbide (SiC) power semiconductors is a further option to improve future SM topologies.