Three-phase electromagnetic filter for zero-sequence harmonics

This paper proposes a shunt electromagnetic filter to attenuate zero-sequence harmonic injection into three-phase star-grounded supplies. The device is built on the basis of zigzag windings and a three-leg core-type magnetic arrangement. Physical considerations as well as mathematical modeling and computer implementation are fully described. The paper reports on computational investigations to verify the filter performance under balanced and unbalanced supply voltages and on laboratory validation of a prototype device. Both the modeling and the laboratory results are in close agreement and demonstrate the capacity of the equipment to filter the components of the zero-sequence currents. The product performance in a real system is also included in the analysis. The theoretical and practical studies show that the level of zero-sequence harmonic injected into the mains can be reduced by 80% or more, depending on the control of filter leakage inductance. This method also leads to cheaper, simpler, and more robust equipment.