Improving the Performance of a Four Branch Passive Filter Using a Zero Sequence Blocking Transformer

It is a known disadvantage of passive filters that their effectiveness in a distribution network is dependent on the source impedance. This is the case with the double tuned four branch, shunt, passive filter, whose performance, at the zero sequence harmonic, is poor due to low zero sequence source harmonic impedance. In this paper, it is experimentally demonstrated that the performance of the filter can be significantly improved by increasing the zero sequence impedance of the source. This is done by placing a zero sequence blocking transformer in series with the source and a four branch, shunt passive filter across the line to simultaneously filter a zero and a nonzero sequence current harmonic from three balanced single phase nonlinear loads.