Modulating functions method plus SOGI scheme for signal tracking

The number of equipments based on static converters such as uninterrupted power systems, series or shunt compensators and distributed generations systems is increasing in the actual power distribution systems. For a correct operation in grid connected condition, these equipments need the information about amplitude, phase angle and frequency of the grid fundamental voltages and currents. Since noise as harmonic pollution and frequency variations are common problems in the utility grid, then it is necessary to have systems able to extract information about the fundamental values from highly distorted signals. For these reasons, robust and accurate estimation and synchronization methods are necessary to obtain the above information also in noise environmental. In this paper, a simple and robust method for frequency estimation based on modulating functions is presented; moreover it is used in addition to an orthogonal system generation method based on the second order generalized integrator (SOGI). The combined use of the two methods has the advantages of a fast and accurate signal tracking capabilities and a good rejection to noise due to the low-pass filter properties of the modulating functions. The effectiveness of the proposed method is validated through simulated experiments and comparisons.