Modular multilevel DC-DC converters interconnecting high-voltage and medium-voltage DC grids

  • Modulare mehrstufige Gleichspannungswandler zur Verbindung von Hochspannungs- und Mittelspannungs-Gleichstromnetzen

Cui, Shenghui; de Doncker, Rik W. (Thesis advisor); Marquardt, Rainer (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2019)
Book, Dissertation / PhD Thesis

In: E.ON Energy Research Center : PGS, Power Generation and Storage Systems 68
Page(s)/Article-Nr.: 1 Online-Ressource (vi, 124 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2019


This dissertation proposes an isolated bi-directional soft-switching dc-dc converter for interconnection of medium-voltage (MV) dc distribution grids and high-voltage (HV) dc transmission grids. The proposed converter combines parallel-connected two-level converters (TLCs) on the MV side and a modular multilevel converter (MMC) on the HV side, and it is named the TLC-MMC converter. A dedicated operation method of the TLC-MMC converter is developed, whereby a certain reactive current is injected into the MV side by the MMC to realize soft-switching operation and low total device ratings of power-semiconductor devices (PSDs) in the TLCs on the MV side. Compared to the existing topologies dedicated to this application, the TLC-MMC converter presents significantly reduced active and passive components and lower PSD losses over a wide power range at variable input and output voltages. The topics on topology, control, and fault-tolerant operation of the TLC-MMC converter are covered in this dissertation with simulations and experimental verifications by a down-scale prototype.


  • E.ON Energy Research Center [080052]
  • Chair of Power Electronics and Electrical Drives [614510]
  • Institute of Power Electronics and Electrical Drives [614500]