Control method and characteristics of active power filters

The authors describe a control method with a combined filter system employing a current source converter and a high pass filter which senses load current, source current and line voltage to create reference signals for an active filter. The transfer function of the active filter is identified and is used for the control system design. It is shown that the source current feedback is most effective to suppress the harmonic-enlarging effects due to parallel resonance and the harmonic current generated by source harmonic voltages. A small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results