A Simple Structure for Accurate Estimation of Single-Phase Grid Frequency Under DC Offset and Both Odd and Even Harmonics

This article proposes an enhanced frequency-locked loop method for the single-phase grid frequency estimation under dc offset and both odd and even harmonics conditions. The proposed method relies on an adaptive recursive discrete Fourier transform-based frequency error detector and an integral controller. It offers a relatively simple structure and computationally efficient method. It can provide accurate frequency estimation at steady state under grid disturbances and takes a dynamic time of around one and half cycles of the fundamental frequency. The improved performance of the proposed method is verified by comparing it with the results of several existing methods reported in the technical literature. The efficacy of the proposed method is proved using simulated and real-time experimental results.