This paper proposes a hybrid active filter for damping of harmonic resonance in industrial power systems. The hybrid active filter consists of a small-rated active filter and a 5th-turned passive filter. The active filter is controlled to behave as a variable resistor by adjusting a feedback gain which changes from a negative to positive value. The negative resistance cancels a positive resistor inherent in the passive filter, so that the hybrid active filter acts as an ideal passive filter with infinite quality factor. This results in a significant improvement of harmonic damping accompanied by harmonic mitigation, 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.
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Fujita et al. (1998) studied this question.
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