Operational Analysis and Modulation Control of Three-Level Z-Source Inverters With Enhanced Output Waveform Quality

Three-level Z-source inverters are recent single-stage topological solutions proposed for buck-boost energy conversion with all favorable advantages of three-level switching retained. Despite their proven buck-boost capability, existing three-level Zsource inverters are either too costly with numerous passive LC elements needed or poor in spectral quality if the "reduced element count" (REC) variant is used. Instead of being constrained by the tradeoff, this paper proposes an alternative three-level Z-source topological and control combination that can produce optimal output waveform quality while using lesser passive LC elements. Through detailed operational analysis, new operating modes of the REC Z-source inverters are identified, which when inserted appropriately to the inverter state sequence will always produce the desired voltage transfer gain with minimized commutation count and optimized three-level switching. For conceptual verification, an optimally controlled laboratory prototype was constructed and tested with a set of results captured and presented in a later section of the paper.