Frequency and Amplitude Tracking of Time-Varying Harmonics and Interharmonics in Power Systems

The paper is focused on monitoring operations performed in power systems. The attention is paid to slow variations characterizing frequency and amplitude parameters of sinusoidal components. A suitable digital signal processing method aimed at estimating frequency and amplitude variations characterizing both the fundamental component as well as single harmonics and interharmonics contained in distorted waveforms is presented. To track time-varying frequency the method first detects the phase deviations of the sinusoidal input with respect to the expected linear trend, and then evaluates the time derivative. In parallel, to track amplitude fluctuations the method takes the square root of the quadratic summation of input sinusoidal projections on two orthogonal references. Distributed filtering operations grant the capability of distinguishing and separately analyzing close-to-each-other components; phase unwrapping allows components affected by significant frequency variations to be tracked