Unified active power filters for source voltage unbalance/current harmonics compensation and power factor correction

This paper presents a unified control scheme for series-type active power filter combined with shunt passive filter to compensate the source voltage unbalance/current harmonics and to correct the power factor simultaneously. The phase angle and the reference voltage for unbalanced voltage/current harmonics compensation are derived from the positive voltage sequence component out of the unbalanced source voltage by using digital all-pass filters. The power factor compensation is achieved by controlling the amplitude of reactive power current in a series filter as zero in synchronously rotating reference frame. Finally, the unified controller output voltage is composed of source voltage unbalance/current harmonics compensation term and power factor correction term. Thus, the proposed algorithm successfully compensates the source voltage unbalance/current harmonics and the power factor. The validity of the proposed scheme has been verified for actual 3 kVA hybrid active power filter system.