UC Irvine

Derived from classic DC-AC multilevel converters, hybrid multilevel converters can combine distinct advantages, thus receiving increasing attention for their widespread industrial applications recently. The Active Neutral Point Clamped (ANPC) converter offers redundant switching states to achieve a better control and more even loss distribution compared to Neutral Point Clamped (NPC) converter. However, in terms of five-level converters, currently the only topology applied in industrial application is the Flying-Capacitor based Neutral Point Clamped converter (FCANPC), which gives a relatively good performance with a simple structure. Despite its advantages, the uneven loss distribution cannot be disregarded as a substantial drawback to affect the power processing capability. The Dual Flying Capacitor Neutral Point Clamped (DFCANPC) converter has been newly proposed to provide better loss balancing and "soft commutation" to have a higher power capability and efficiency.

In this thesis, traditional multilevel topologies such as Cascaded H-Bridge converter, Diode Clamped converter, and Flying Capacitor converter are summarized, followed by popular modulation schemes including carrier-based modulation, Space Vector Modulation and Selective Harmonic Elimination modulation. Thermal models and cooling strategies are then briefly discussed. As the main focus, thermal analysis and comparison regarding the five-level FCANPC converter and the newly proposed DFCANPC converter is reported in this thesis. A PSIM model has been built for verification of loss balancing performance of the DFCANPC converter.