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A Novel Single-Phase Bidirectional Nine-Level Converter Employing Four Quadrant Switches

A novel bidirectional ac-dc multilevel converter based on four quadrant switches is proposed. This new converter can establish nine voltage levels downstream the coupling filter used to interface with the power grid, and, comparing with conventional two- or three-level converters, it operates with improved ac-side current, both for operation as active rectifier (on-grid), grid-tied inverter (on-grid) or voltage inverter (off-grid). A detailed description of the converter is exhibited, highlighting its main advantages according to the applications where it can be employed in smart grid scenarios. In order to confirm its viability, a considerable set of results is presented and discussed, establishing an overall comparison with conventional converters. Moreover, the proposed converter is validated operating as active rectifier, as grid-tied inverter, and as voltage inverter, controlled in closed-loop by current or voltage. The details ofthe proposed power converter hardware and the implementation of the digital algorithm, based on a fixed switching frequency structure, are clarified and discussed throughout the paper.