Design of harmonic current detector and stability analysis of a hybrid parallel active filter

A promising method to solve harmonic problems in power systems is by using a hybrid parallel active power filter. This filter is composed of both active and passive filters. The active filter will suppress low-order harmonic currents of the power system and the remaining high-order harmonic currents in the system will be reduced by a high-pass passive filter. In this hybrid structure, one has to consider both the detection method for harmonic current to be compensated by the active filter and the stability in the presence of the passive filter. In this paper, the authors present a new design method for a harmonic current detector which will detect, precisely, the low-order harmonic currents (5^th, 7^th) using a band-pass filter built on the rotating frame of the fundamental frequency (50 Hz). In addition, stability analysis of the whole system when the point of detection is located at various positions is investigated. Experimental results shown in the paper indicate the effectiveness and validity of the method proposed