Effectiveness of resonant harmonic filters and its improvement

A low impedance path created by a resonant harmonic filter reduces the supply current harmonics to which the filter is tuned, if these harmonics are caused by the load, but increases them if they are caused by the distribution voltage harmonics. Moreover, due to filter resonance with the distribution system inductance, some harmonics, other than characteristic ones, could be amplified. Consequently, minor harmonics, which are omnipresent in distribution systems now due mainly to an increasing presence of power electronics equipment, are causing filters to lose their effectiveness. The filter may even increase the waveform distortion. This paper investigates degradation of the filter performance by minor voltage and current harmonics. The paper demonstrates that the filter effectiveness can be improved by an optimization procedure that takes into account the presence of harmonics in the distribution voltage and minor harmonics in the load current. The paper describes this procedure and, using computer simulation, shows to what degree the filter effectiveness can be improved.