Z-Source Multilevel Inverters

There are two hotly researched Z-source/quasi-Z-source (ZS/qZS) multilevel inverters: the ZS/qZS neutral-point-clamped (NPC) inverter and ZS/qZS cascaded multilevel inverter (CMI). The ZS/qZS concept, integrating with those traditional multilevel inverters, inherits the merits of both topologies with improved inverter reliability due to short-circuit immunity. This chapter presents the configurations, operating principles, and modulation schemes of the two ZS/qZS multilevel inverters. Three-level NPC inverters, having many inherent advantages, are commonly used as the preferred topology for medium voltage ac drives. The CMI is a promising candidate for the next generation of PV power converters because it has features such as separate PV sources, transformerless, low harmonics, small filters, and low switching frequency. The system-level modeling and control of a qZS-CMI-based three-phase grid-tie PV power system were addressed, and simulation results were demonstrated, providing a competitive candidate for high-power medium-voltage power systems.