A chirp-z transform-based synchronizer for power system measurements

In the last few years, increased interest in power and voltage quality has forced international working groups to standardize testing and measurement techniques. IEC 61000-4-30, which defines the characteristics of instrumentation for the measurement of power quality, refers to IEC 61000-4-7 for the evaluation of harmonics and interharmonics. This standard, revised in 2002, requires a synchronous sampling of voltage or current signal, in order to limit errors and to ensure reproducible results even in the presence of nonstationary signals. Therefore, an accurate estimation of the fundamental frequency is required, even in the presence of disturbances. In this paper, an algorithm to detect the fundamental frequency is proposed; it is based on the chirp-z transform (CZT) spectral analysis and is able to observe all standards in force because of its accuracy and working characteristics. Theoretical aspects are discussed and various experimental tests are reported, comparing the proposed method with a similar well-known one based on interpolated fast Fourier transform (FFT) analysis. Finally, a complete characterization of the proposed system was performed, and its accuracy was evaluated by means of a calibrator.