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 Z-source inverters are either too costly with numerous passive <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> elements needed or poor in spectral quality if the ldquoreduced element countrdquo (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 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> 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.