Multifunctional strategy for four-leg grid-tied DG inverters in three-phase four-wire systems under symmetrical and asymmetrical voltage conditions

This paper investigates connecting renewable energy sources such as solar, wind and the others to the microgrids through power electronic interfaces for active power provision and also harmonic, unbalance, and reactive power compensation under both symmetrical and asymmetrical voltage sources. The four-leg converter topology is applied because of its better controllability in four-wire systems applications. Two instantaneous current decomposition techniques, namely conservative power theory and instantaneous power theory are studied to show the similarities and differences between these techniques from performance perspective in active power filter. The studied system is a three-phase four-wire grid which includes unbalanced and non-linear loads, and has negligible line impedances. The control strategy is implemented in abc-frame which allows for selective load current provision by distributed generators interface converters. The principles supporting the developed control strategy are discussed and the results are demonstrated through digital simulations conducted by means of PSIM.