Comparison and implementation of a 3-level NPC voltage link back-to-back converter with SiC and Si diodes

This paper presents a high efficiency 10 kVA high-frequency input and output Si IGBT and SiC Schottky diode 3-level neutral point clamped voltage dc-link back-to-back converter (3LNPC-VLBBC). A switching frequency of 48 kHz makes the converter suitable for driving high-speed and low-inductive machines. A detailed loss analysis reveals that only four of the six diodes in a 3-level bridge-leg have to be replaced by SiC diodes to enable high efficiency operation if an appropriate modulation scheme is used. A comparison with an All-Si 3-level converter shows a reduction of the semiconductor losses by 10% at the nominal operating point. In addition, a semiconductor chip area based comparison is presented, showing the chip area partitioning of the individual semiconductor types and the corresponding costs for different implementations. The payback time for the additional costs resulting from replacing the Si diodes in the 3-level converter by SiC diodes due to energy savings is estimated. Finally, experimental results of the prototype are provided.