Influence of A/D quantization in a renewable energy system using a DFT based estimation of grid signal parameters

A photovoltaic system is one of the most widely used systems in the green energy production. An estimation method of grid signal parameters (frequency, amplitude, phase) is a very important issue in the control of such a system. This paper presents the influence of the number of A/D converter bits b, the width of the measurement window relative to the grid signal period, and the number of samples N obtained in the measurement window on the results of a newly developed estimation method based on the FFT procedure. An increase in the number of b by 1 decreases estimation errors approximately twice. Estimation errors are the sum of the systematic error (inversely proportional to the N^4 value) and the error caused by the quantization noise (inversely proportional to the square root of the N value). In practical applications (N=32, ..., 2048; b=8, ..., 24), the dominant component is the error caused by the quantization noise. Before the estimation process, a proper filtering should be done.