A new digital filter for phasor computation. I. Theory [powersystem protection]

摘要

A new pair of orthogonal filters for power system phasorncomputation is presented. They have excellent time-frequencyncharacteristics for fault location and measurement. Their impulsenresponses are obtained applying the inverse Fourier transform to ansingle-lobe function with a strong stopband. From this process, a newnwindow emerges. Without side lobes, it overcomes the temporal barriersnimposed by the rectangular window, implicit in digital Fouriernfiltering. Its length is not restricted to a multiple of one cycle, andnit can be adjusted to cover totally the available samples of the fault,nextracting the fundamental component with growing precision. On thenother hand, its sampling frequency can be reduced to twice thenfundamental frequency. In particular, at this minimum samplingnfrequency, the digital Cosine filter rejects the even harmonics and thenaperiodic component