THD ESTIMATION BY NON-COHERENT SAMPLING USING VARIOUS DSP ALGORITHMS AND WINDOWS

Martin Novotny, Milos Sedlacek

Abstract

The paper aim inspects influence of the used RMS-value computing algorithm type and of window type and order on estimation of signal total harmonic distortion (THD). The THD relative bias is investigated by means of computer simulations in MATLAB. A test signal containing the fundamental and 12 higher-order harmonic components with magnitudes corresponding to an international compatibility levels standard and corresponding to the THD of approximately 11 % is used. Three algorithms of THD estimation are investigated, differing in total RMS value and the fundamental component’s RMS value estimation. The total RMS value is found either in time domain or in frequency domain, and the fundamental component RMS value is found either by processing signal components in the used window spectrum main lobe, or using DFT interpolated in frequency domain. Influence of energy leakage for non-quantized test signal and of the 1st order and the 3rd order cosine windows is investigated. The influence of signal quantization for the 12-bit and 16-bit ADC and the above-mentioned windows is also shown. Also the influence of phases of test signal harmonic components by THD estimation by non-coherent sampling using the three investigated algorithms and expression for THD uncertainty caused by quantization is presented.

Download

IMEKO-TC4-2008-016.pdf

DOI

-

IMEKO TC

TC4 - Measurement of Electrical Quantities

Back to the proceedings