A novel and small-capacity neutral line active power filter in three-phase four-wire system

The unbalanced and nonlinear loads could result in a significant neutral current in the three-phase four-wire distribution power system. This paper proposes a novel neutral line active power filter (APF) system based on the special connection of the transformers and single-phase inverter. The theory analysis and computer simulations show that: (a) control system would be easy to implement due to only one single-phase inverter exists, (b) harmonic compensation efficiency is higher than 90% and the fundamental current in the neutral line would not be affected, (c) the VA rating and cost of the inverter are significantly reduced compared to the conventional three-phase four-wire APF system.