Hybrid Neutral Point Clamped Converter: Review and Comparison to Traditional Topologies

In applications such as transportation electrification, there are strict requirements regarding efficiency, reliability, power density, and cost. Therefore, a diverse array of circuit topologies which can be selected and tailored for specific requirements is desirable. Hybrid topologies are particularly valuable in this regard because hybrid topologies can combine the attributes of traditional multilevel converter (MLC) topologies, such as cascaded H-bridge (CHB), flying capacitor (FC) converter, or three-level (3L) neutral-point-clamped (NPC) converter. A hybrid topology which has obtained substantial popularity combines NPC with FC to form the five-level active NPC (5L-ANPC) topology. The popularity of 3L-NPC and 5L-ANPC has been encouraging researchers to develop other hybrid MLC topologies. Therefore, to establish the present state of the art of hybrid NPC topologies, a literature review is conducted. Based on the results of the literature review, several figures of merit (FOMs) are derived to objectively compare the system-level attributes of this class of power circuit topologies. These FOMs are also compared with traditional topologies to demonstrate the utility of hybrid NPC topologies in terms of efficiency, power density, and cost. This work will serve as a selection guide for future design efforts considering hybrid NPC topologies.