Utilization of a neutral wire filter inductor in a three-leg four-wire active power filter

Three-leg active power filter topology is the cost effective solution implementing a four-wire active power filter but it has some disadvantages compared to four-leg topology. The lack of a neutral wire filter inductor results in larger filter losses and therefore the efficiency of the topology is impaired. The neutral wire filter inductor is typically used with the four-leg four-wire active power filter topology and significantly reduces switching frequency current ripple. In this paper the suitability of a neutral wire filter inductor for the three-leg topology is studied. The performance of three-leg topology with a neutral wire filter inductor is studied through computer simulations and laboratory tests. The results indicate that the use of the neutral wire filter inductor clearly improves the performance of three-leg topology.