Control strategy and space vector modulation for three-leg four-wire voltage source inverters under unbalanced load conditions

One of the desirable characteristics of inverters in three-phase systems is the ability to feed unbalanced/non-linear loads with voltage and frequency nominal values. Therefore three-leg four-wire inverters are expected to play an essential role in future power systems because of their ability to handle the neutral current caused by unbalanced or non-linear loads. This study introduces an original control method in combination with three-dimensional space-vector modulation (3D-SVM) strategy. The steps for the 3D-SVM implementation are identified. The switching vectors, 3D-SVM diagrams and the boundary planes equations, as well as the matrices for the duty cycles and symmetric switching sequences are discussed in detail. Experimental results including different loads are presented to validate the proposed SVM control strategy for three-leg four-wire voltage source inverters. The experimental results of this study show that the developed control scheme in combination with three-leg four-wire inverters can carry out the grid feeding requirements and supply good power quality to loads under extreme unbalanced conditions efficiently.