Comparative Analysis of Techniques for Reducing the Signal Parameters Measurement Error for the Quadrature Demodulation Application

At present the methods of measuring signal parameters based on the spectrum analysis are highlighted by their universality. It is known that using the values of the complex spectrum it is possible to calculate the remaining parameters indirectly. All indicators of the electrical power quality can be measured through the values of the signal spectrum. DFT-based algorithms are mostly used to determine the spectrum in practice. These algorithms are very famous, and the problems associated with their usage in the conditions of the finite deviation of the signal frequency are known as well: the appearance of the “spectrum spreading” effect. In practice it is difficult to resist this effect, especially in case of using the fast Fourier transform algorithms. The alternative solution is to use the quadrature demodulation method. This approach also allows to obtain samples of the complex spectrum and has the significantly higher accuracy compared to the traditional DFT algorithms. The article considers the method of quadrature demodulation in relation to the measurement of the main parameters of the signal: amplitude value, phase value and frequency. The obtained relations allows to estimate the measurement errors of the frequency, amplitude and initial phase when measured by the quadrature demodulation method. The basic regularities of their behavior by time are specified. The methods of the resisting to the variable component of the methodological error of these parameters are suggested. For the inaccuracy reducing it is offered to perform the post-filtering of the measurement results of the considerate parameter.