| Abstract |
Characteristics of some power engineering signals in variable-speed drives are described. Terminology
for non-sinusoidal voltages and currents, and FFT (Fast-Fourier-Transform) signal processing, were expanded in our
R&D work on drives for both industry and traction. Solutions of the necessary potential isolation as well as some
V-A-W-meters was dealt with. It was recently found that this could be of interest to the public that so far are basing their work on the well-established Fourier-Series analysis and thereby neglecting sub-harmonics as well as interharmonics and some phase shifts. Our experience is that we can rely on modem signal processing with autocorrelation and cross-correlation to define RMS-values, as well as active, reactive and apparent power. The result is
a linear method to handle the frequency components of the three power quantities "P", "Q" and" S= P+jQ"- as long
as we do not pass through a frequency inverter. RMS-values "IRMs" and "URMs" must on the other hand be handled
especially. The Hilbert transform of the current is basically used to define reactive power. The coherence function
which is a statistical function of the frequency is a proper quantity to analyze the uncertainties in the three power
quantities mentioned above. Furthermore, we found that earlier definitions of apparent power and distortion power are non-stringent while the definitions reported in the paper are in full accordance with the methods implemented in modem dynamic signal analyzers. One should not define S = URMs · IRMs any more for non-sinusoidal systems. |
