Attenuating Null Current by Single-phase Inverter in Three-phase-Four-Wire Distribution Power Systems

Nowadays the three- phase-four-wire systems are widely used in low voltage applications. However these systems have serious problems of harmonic and neutral line current contamination. Harmonics that are cause by the existence of non-linear loads in the system affect the amount of current passing through the neutral line in the distribution system. In this paper a neutral line attenuator is proposed to solve the neutral current problem. This attenuator includes a zero sequence transformer, a single-phase power converter and a diode as a rectifier. Two single-phase transformers with the winding ratio 1:1 is used as zero sequence transformer each one of which are connected to the each line of three- phase-four-wire distribution system to supply the zero sequence current. There is a single-phase power converter between zero-sequence transformer and the neutral line that acts as a resistance in the neutral line. Also a rectifier with low maximum power rating is connected to the DC bus of single-phase power converter to overcome the convertor power dissipation and maintain constant voltage. The results of computer simulations show that the proposed neutral current attenuator has achieved the expected performance.