Robust frequency-estimation method for distorted and imbalanced three-phase systems using discrete filters

The continuous monitoring of voltage characteristics in electric power systems, such as in microgrids, is required for power quality assessment, grid control, and protection purposes. Due to the presence of disturbances in the grid voltage, such as harmonics, imbalances, noise, and offsets introduced by the instrumentation, among others, the frequency-estimation process has to be robust against all these disturbances to obtain an accurate estimation of the frequency value. This paper presents a fast and accurate method to estimate the fundamental frequency of an electric power system. The estimation method works properly in balanced and imbalanced three-phase systems, and even in single-phase systems. The proposed solution is based on an algebraic method, which is able to calculate the frequency of a pure sinusoidal signal using three samples. A filtering stage is used to increase the robustness of the algorithm against disturbances in a wide frequency range. Simulation and experimental results show the good performance of the method for single- and three-phase systems with a high level of harmonic distortion, even in the presence of amplitude, phase, and frequency changes.