Improving the performance of a three-leg four-wire active power filter with a neutral wire filter inductor

In this paper the suitability of a neutral wire filter inductor for a three-leg four-wire active power filter (APF) topology is studied. The study is based on computer simulations and laboratory tests. The neutral wire filter inductor is typically used with a four-leg four-wire APF topology and it significantly reduces switching frequency current ripple. In the case of the three-leg topology, the lack of neutral wire filter inductor results in greater line filter losses and therefore the efficiency of the topology is lower. The results indicate that the use of the neutral wire filter inductor clearly improves the performance of the three-leg topology but the complete suppression of the switching frequency current ripple requires the use of more efficient passive filter structures.