Thermal and Performance Comparison of Active Neutral-Point-Clamped (ANPC) and Dual FlyingCapacitor ANPC (DFC-ANPC) Inverters

Multilevel inverters provide advantages such as improved efficiency, superior thermal characteristics, a better distribution of switching and conduction power losses, smaller size of passive components including ac filters and EMI filters, as compared to their two-level counterparts. Flying-capacitor (FC)-based multilevel inverters are gaining more attentions, and finding lots of medium-voltage as well as low-voltage industrial applications. Active neutral-point-clamped (ANPC) inverter, as a derived topology from FC-based inverters, offer the advantages of a reduced number of FCs as well as fewer switching cells. However, ANPC inverter needs high-voltage line-frequency switches which makes it difficult to increase number of levels/cells especially to more than five levels. The dual flying-capacitor (DFC)-ANPC topology addresses this by allowing the use of lower voltage power switches in series to replace high-voltage switches due to its feature to have natural zero voltage switching for line-frequency switches. This paper compares the ANPC and DFC-ANPC inverters in terms of high-voltage line-frequency power switch requirements and their practical implementation. Additionally, thermal comparison of both inverters running at low and high modulation indexes is provided, which further verifies the superior performance of the latter topology.