Method of Reducing of the Complex Spectrum Measurement Error In Case of Applying of the Quadrature Demodulation Technique

Abstract

The quadrature demodulation technique can be applied to measure the frequency, amplitude and phase spectrum of electric power grid signals. This measurement method has a number of advantages: simplicity of analysis of measurement error, the ability to increase the measurement accuracy (by applying a higher order digital filter), and simplicity of simulation. One of the disadvantages of this method is the relatively large dynamic error component caused by the application of post-filter or by the reference frequency adjustment (both approaches allows to reduce the signal parameters measurement error). In this paper we propose an alternative approach that makes it possible to achieve a significant reduction of the measurement error without increasing the filter order. For the proposed approach, an increase of the dynamic error component is not observed. The proposed approach consists in compensating the amplitude and phase spectrum measurement results by applying analytical dependences and frequency measurement results. In this paper, analytical expressions are obtained that make possible to estimate the maximum value of the spectrum error in case of applying the proposed approach. The influence of the frequency measurement error on the accuracy of the proposed method of the spectrum measurement error correction is estimated. By Matlab and Simulink software, a simulation modeling has been performed, which makes it possible to assess the reliability of the obtained analytical expressions and the effectiveness of the proposed approach. When performing simulation, sinusoidal, polyharmonic (line spectrum) signals and a sinusoidal signal distorted by white noise are considered.