Current Regulation in Four-Leg Voltage-Source Converters

Three-phase four-leg voltage-source converters by virtue of the fourth leg connected to the neutral points of the wye-connected loads effectively handle the zero-sequence currents and voltages occasioned by connected load impedance imbalances and/or nonlinearity of loads. This paper develops a generalized carrier-based pulsewidth-modulation scheme for this converter which with a natural reference-frame control scheme that directly controls the actual load currents ensures current regulation irrespectively of the nature of the load. The proposed modulation and control schemes are effectively validated by computer simulation and experimental results for the converter operation in the linear and overmodulation regions.