A practical directional third harmonic hybrid active filter for medium voltage utility applications

An increased level of harmonics due to the proliferation of single-phase non-linear loads is raising serious concerns among utilities. Historically, passive filters have been proposed to reduce harmonics in MV utility applications. However, due to their limitations utilities are turning their attention to alternative solutions. At the same time, active filters are prohibitively expensive and are unlikely to become a realistic solution in the near future. In this paper a practical directional third harmonic hybrid active filter is proposed. A novel feature that adjusts the level of compensation provided by the filter based on the loading conditions of its passive components is introduced. Simulation and experimental results are presented. Issues related to utilizing existing VAr support capacitors for retrofit applications thereby achieving cost reduction and fail normal feature for increased reliability are addressed. Cost vs. performance curves are developed using factual utility harmonic data. Finally, the impact of a distributed filtering solution based on the proposed filter is shown using a simplified MV distribution system.