Correction Methods of the Magnitude Response of the Power Quality Measurement Channel Containing a Sigma-Delta ADC

Currently, the leading manufacturers of integrated circuits produce Sigma-Delta ADCs, focused on the application as a part of a measurement channels of power quality (PQ) instruments. The magnitude response of such an ADC is determined by a built-in digital filter, usually with an cascaded integrator-comb (CIC) filter structure. However, the magnitude response of this filter (from the point of view of the low-pass filter function) do not have the required parameters: the filter has a slope of the magnitude response (MR) in the passband and a relatively large bandwidth between passband and stopband. In this article, two variants of the method for correcting the Sigma-Delta ADC magnitude response which is a part of PQ instrument measurement channel are considered. The first approach involves the application of a single corrective digital filter that compensates the Sigma-Delta ADC passband ripple and reduces the bandwidth between passband and stopband. The second approach involves the application of two corrective digital filters, one of which compensates the ADC passband ripple, and the other one reduces the stopband frequency. Both options considered assume the application of Matlab built-in functions. The methods for calculating the coefficients of the correcting filters are considered for both approaches. By the application of simulation modeling, the characteristics of the PQ instrument measurement channel, which contains the CIC filter and the compensating filter, are obtained. The possibility of modeling the PQ instrument measuring channel in the Simulink software package is considered. The features of modeling of the blocks of the CIC-filter, filter-compensator and data format conversion for the case of the PQ measurement channel are analyzed.