Characteristics of Measurement of Criterion Values and Adaptive - Digital Signal Processing in Power System Protection and Control - page 197

It is evident that when frequency measurement shows its increase it means that
the signal period decreases and filter window should be shorter, and the other way
round when frequency decreases.
Results of the adaptive solution application for measurement of active power
and resistance are shown in Fig. 9.14 . For resistance nothing has really changed
(accurate results were observed also without adaptation on), but now also active
power is measured accurately.
Further advantages of the adaptive methods are visible when some noise is
added to input signals (2nd and 4th harmonic, 0.15 per unit each, Figs. 9.17 and
9.18 for step and linear change of signal frequency). Analyzing the results for
impedance measurement without and with adaptation, one can easily notice
additional effect of decreasing of the errors due to noise for the adaptive solution.
The measurement results are not perfect (the filters might not be exactly matched
to actual cycle of the signals), however, they oscillate quite closely around
accurate values of R, X and Z.
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