Active Voltage Balancing and Thermal Performance Analysis of Dual Flying-Capacitor Active Neutral-Point-Clamped (DFC-ANPC) Inverters

Multilevel inverters provide appealing advantages such as improved efficiency, superior thermal performance, better distribution of the switching and conduction power losses, smaller size of passive components including output ac filters and EMI filters, as compared to their two-level counterparts. The flying-capacitor (FC)-based topologies are attaining more attentions, and are finding lots of medium-voltage and low-voltage industrial and residential applications. The FC-based active neutral-point-clamped (ANPC) inverter, as a hybrid topology based on the three-level ANPC and the FC-based configurations, offers outstanding advantages including the reduced number of FCs as well as switching power cells, improved efficiency, and enhanced power quality. However, the utilization of high-voltage line-frequency switches, as a major drawback, hinders the ANPC converter from expansion and penetration into the high-voltage ranges. The dual flying-capacitor (DFC)-ANPC topology resolves this issue through introducing the zero-voltage-switching (ZVS) feature into the line-frequency devices. This soft-switching makes it possible to use the series connection of several low-voltage devices for the realization of the high-voltage switches without having the transient voltage imbalance issues. This article studies the thermal benefits that are achieved in the DFC-ANPC topology alongside the ZVS operation of its line-frequency high-voltage switches. Furthermore, an active voltage balancing technique, based on logic-equations, is proposed in this article for control of the FCs' voltages. The experimental results are provided to validate the improved thermal performance of the DFC-ANPC topology as well as the active balancing technique for the regulation of the FC voltages.