Considering the increasing demand on digital processing techniques for power electronics and power systems application, this paper deals with the use of a Recursive Discrete Fourier Transform (RDFT) for phase angle, frequency and magnitude identification of the grid fundamental voltages, irrespective to waveform distortions, frequency or amplitude deviations. It will be discussed that if the fundamental frequency of the measured voltages exactly matches the frequency for which the DFT has been designed, an ordinary RDFT algorithm is completely able to provide the necessary information about phase, frequency and magnitude. Two additional algorithms have been proposed to ensure the correct performance if the frequency departs from its nominal value: one for phase correction and another for identification of the fundamental component magnitude. Moreover, it is important to point out that by means of the proposed algorithms, the fundamental component can be identified in less than 2 cicles, independently of the input voltage signal. The analysis of the RDFT has been performed by means of simulation results. In order to evaluate the behavior of the RDFT in a practical system, experimental results regarding to the synchronization of a small generator and the power grid will be presented.
Discrete Fourier Transform; frequency identification; fundamental wave identification; phase detection; recursive DFT; synchronization
