Power Quality Performance of an Active Harmonic Filter with a Power Converter Feeding Magnet Load

In particle accelerator environment, most of the power converters feeding magnet-loads have either thryristorized or diode bridge at their input stage. Loads to these power converters are fixed but they are operated through a wide current range. Such converters being non-linear loads to the mains produce considerable distortion in the supply current. Hereby, results in a poor total harmonic distortion (THDi). An active harmonic filter (AHF) is provided in parallel with the power converter to give a path for the harmonic and reactive current demand of the power converter. The pure AHF scheme implemented using analog control is simple, rugged, and cost effective. In earlier literatures, ways to determine filter ratings of constant power type loads are given. In this paper, apart from describing the filter design and its performance in terms of power quality, a proper way to decide filter rating for the power converters feeding fixed loads like magnets is explained. A prototype 5 kVA AHF design-implementation has brought down THDi to 6.67% from 57.46%.