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Hybrid filter for dynamic harmonics filtering and reduction of commutation notches - a case study

Active filters are today widely-used to improve voltage quality in industrial power grids. They are sometimes considered a generic solution and detailed analysis of the voltage quality in the affected grid is neglected. However, interactions between an active filter and the connected network are always present and may affect filter performance. This paper discusses the interaction of voltage perturbations and active filter systems and presents a case study of a hybrid filter installed in a metal processing plant. The hybrid filter consists of an active filter and a passive voltage notch filter realized through a series connection of resistors and capacitors. It achieves dynamic harmonics filtering and reduction of voltage notches in a low voltage distribution network where severe commutation notches would otherwise prohibit the operation of active filters without additional measures. Discussion of the filter effect is based on power quality measurements.