Evaluation and Performance of Three-Phase Inverter Using Multiple Bidirectional Choppers Intended for 1.5-kVdc PV Systems

Abstract

This article focuses on the chopper-cell number of a novel three-phase inverter for utility-scale photovoltaic (PV) systems where multiple cascaded bidirectional chopper cells and a three-phase line-frequency transformer with a three-legged core are used. The inverter per phase is composed of a main converter, which is equivalent to the conventional bidirectional chopper, and an auxiliary converter, which is composed of multiple cascaded chopper cells. Although the inverter performance can be improved by increasing the chopper-cell number because of increased switching frequency and reduced voltage steps, the increased cell number may result in increased converter loss and cost. However, no paper has evaluated the chopper-cell number of the inverter to the best of the authors’ knowledge. Further, no paper has carried out experimental verification of the inverter during the power faults. This article evaluates the inverter using two cells per phase (two-cell inverter) with the one using three cells per phase (three-cell inverter) under the same equivalent switching frequency in terms of converter loss, efficiency, and steady/transient state performance. The numerical analysis shows that the two-cell inverter shows superiority over the three-cell inverter in converter efficiency. Further, the experiments using a 1.5-kW downscaled model verify the inverter performance under the normal and fault conditions.