Abstract: Currently, among the parameters of signals of industrial networks, the most interesting are such parameters as rootmean-square (RMS), active, reactive and apparent power. Since most devices that are loads for such networks are non-linear loads, the waveform of voltage and mostly of current is distorted. Real voltage and current belong to the class of polyharmonic signals: contains spectral components (harmonics), that are multiples of the main frequency of the signal. The known methods for measuring the RMS, amplitude spectrum, active, reactive and apparent harmonic power for the case of polyharmonic signals are based on the determination of the complex voltage and current spectra. The paper considers the measurement of the spectrum of electrical signals by the method of quadrature demodulation. The main sources of measurement error are: the amplitude-frequency characteristic of the output filter of the demodulator, the presence of other harmonics in the signal spectrum, the deviation of the frequency of the input signal from the nominal value. In this paper, we consider the influence of the used filters of various types (IIR, FIR and cascadecomb) on the value of the measurement error of the amplitude spectrum. Simulation modeling was performed in Matlab and Simulink programs. The results of simulation modeling were obtained for each of the considered filter types for the following cases: input signals are sinusoidal; input signals are polyharmonic; input signals are sinusoidal with white noise distortion. For the case of sinusoidal input signals, the effect of the frequency deviation of the input signal from the nominal value is considered. Comparison of the used filters is made in terms of implementation complexity and measurement error. It is shown that among the considered filters the smallest error in measuring the amplitude spectrum can be achieved with the use of cascaded-integrators-comb filters (CIC). From the point of view of hardware implementation among the filters considered, the most simple is the CIC. To improve measurement accuracy — to reduce the bandwidth unevenness of the resulting filter — an additional FIR filter compensator can be used.
Index terms: spectrum of electrical signals, quadrature demodulation, digital filtering, cascaded-integrator-comb.


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