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

This paper proposes a hybrid active filter for damping of harmonic resonanc e in industrial power systems. The hybrid filter consists of a small-rated active filter and a 5th-tuned passive filter. The active filter is characte rized 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 res istor by adjusting a feedback gain from a negative to positive value, and v ice versa, The negative resistor presented by the active filter cancels a p ositive resistor inherent in the passive filter, so that the hybrid filter acts as an ideal passive filter with infinite quality factor. This signific antly improves damping the harmonic resonance, compared with the passive fi lter 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 vi ability and effectiveness of the hybrid active filter proposed in this pape r.