Detection of unstable low frequency oscillations based on PMU measurements

A new algorithm based on wide area measurements and Discrete Wavelet Transform (DFT) to detect the unstable low frequency power swing oscillations of synchronous generators in a power system is proposed. The PMU modules calculate and transmit the synchronized phasor values of generator voltages, currents and speed to Phasor Data Concentrators (PDC) where data are collected and analyzed. Generators rotor angle change is estimated in PDC center by means of generator speed. For each generator, the Lyapunov´s relative energy function, which is the sum of its relative potential and kinetic energy, is calculated. After that, the generator instability is determined from computing and comparing the energy stored in some decomposed levels. The method is simulated on a network containing of two generators with some simulated stable and unstable low frequency oscillations.