Three-Phase Four-Wire Inverters Based on Cascaded Three-Phase Converters With Four and Three Legs

In this paper, a generalization for three-phase four-wire inverters is proposed. In this generalization, an arbitrary number of three-phase four-wire dc–ac converters are cascaded by means of injection transformers, in order to compose a resultant inverter with a single dc link. Its converters may have four or three legs composed by a pair of the complementary insulated-gate bipolar transistor. The injection transformers have different turns ratios calculated in order to maximize the number of levels produced in the output voltage. In this way, the converter cells within the inverter are asymmetrical in terms of power rating. In this paper, the proposed generalization is applied to a specific case, where two four-wire converters are cascaded, which generates four different proposed configurations. These configurations are analyzed in detail and compared with the conventional four-leg inverter by means of data acquired from simulation and experimental results. In these results, the proposed and conventional inverters feed an unbalanced three-phase load accordingly to the same reference voltage, and the load current total harmonic distortion, voltage weighted total harmonic distortion, transformers and semiconductors losses, switching frequency, and power rating are analyzed in order to conclude that proposed configurations present better performance, even though they have more semiconductors and demand injection transformers.