A hybrid active filter for damping of harmonic resonance in industrial power systems

TLDR

The study proposes a hybrid active filter to damp harmonic resonance in industrial power systems. The hybrid filter combines a small‑rated active filter that senses 5th‑harmonic current and switches between negative and positive resistance via feedback gain with a 5th‑tuned passive filter, enabling the active component to cancel the passive filter’s inherent resistance and achieve an ideal passive filter with infinite quality factor. Experimental results on a 20‑kW laboratory model show that the hybrid filter markedly improves resonance damping versus a passive filter alone and limits excessive harmonic current by acting as a positive resistor.

Abstract

This paper proposes a hybrid active filter for the damping of harmonic resonance in industrial power systems. The hybrid filter consists of a small-rated active filter and a 5th-tuned passive filter. The active filter is characterized by detecting the 5th-harmonic current flowing into the passive filter. It is controlled in such a way as to behave as a negative or positive resistor by adjusting a feedback gain from a negative to positive value, and vice versa. The negative resistor presented by the active filter cancels a positive resistor inherent in the passive filter, so that the hybrid filter acts as an ideal passive filter with infinite quality factor. This significantly improves damping the harmonic resonance, compared with the passive filter used alone. Moreover, the active filter acts as a positive resistor to prevent an excessive harmonic current from flowing into the passive filter. Experimental results obtained from a 20-kW laboratory model verify the viability and effectiveness of the hybrid active filter proposed in this paper.