Optimizing the Series Active Filters Under Unbalanced Conditions Acting in the Neutral Current

This paper discusses the limitations of the series active power filter operating in unbalanced three-phase four-wire systems and proposes the insertion of series active impedance to neutral wire. The control of this active impedance uses a modified synchronous reference frame controller (MSRFC) in order to mitigate the flow of zero sequence harmonic components. The performance of the combined system, constituted of two series active filters, is simulated with and without the insertion of a series active filter to the neutral wire and the results arc presented. The simulation confirms the viability of proposition and the discussions show the importance of using this proposed structure when series active filters, based on three-phase synchronous reference frame controller (SRFC), is used as control strategy in unbalanced four-wire systems.