Abstract
The advent of the Modular Multilevel Converter technology allows building multi-terminal high-voltage DC grids. In order to interconnect DC grids with different voltage levels, highly efficient and compact high-voltage DC-DC (HVDC) converters are required. This paper presents the control and design of a transformerless high-voltage DC-DC converter, which has been designed and built within the framework of the research project GriDConv at the Graz University of Technology. The converter basically consists of high-voltage half-bridges in combination with a series of submodules with full-bridge technology. A dedicated control strategy for the converter is developed, which allows advantageous soft switching of the high-voltage half-bridges, which considerably reduces switching losses of the half-bridges. In addition, a balancing strategy for the individual cell voltages as well as a control of total cell voltage are presented. The developed control strategies are discussed in detail and, in the end, verified through experiments on a constructed 50,text{k}text{W} lab-scale hardware demonstrator.
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