Power losses evaluation of three multilevel converter topologies for direct interface with medium voltage grids

This paper presents the power losses evaluation and comparison of three different Mega Watt MW scale multilevel converter topologies proposed for interfacing energy storage systems to medium voltage grids using Medium Frequency Transformers MFTs to provide the galvanic isolation. The candidates are the Hybrid Cascaded H Bridge HB Multilevel Converter HCHB-MLC topology, the second is an Unfold Cyclo-converter cell based Multilevel Converter UFCYC-MLC topology and the third is a proposed Folded Cyclo-converter based Multilevel Converter FCYC-MLC topology. Detailed electrical and dynamic thermal models of the converters´ power electronics circuits are implemented and simulated using the PSIM. The semiconductor power losses of the various converters components and the power losses of the DC-link capacitors and the MFTs are evaluated using the simulation waveforms obtained at the nominal voltage of the converters and at different loading currents for the full range of the power factor. The results show that the HCHB-MLC topology gives the highest efficiency for a wide range of loading condition and the proposed FCYC-MLC topology is found more efficient than the conventional UFCYC-MLC.