The on-Line Monitoring of Time-Varying Amplitude and Frequency Characteristic of Sub-Synchronous Oscillation Based on Sliding Window FFT

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Abstract
With the continuous increase of wind power grid-connected capacity, the random fluctuation of wind power makes subsynchronous oscillations (SSO) exhibit time-varying amplitudes and frequencies characteristics. This paper proposes an on-line monitoring method to identify subsynchronous oscillation modals (including frequencies, amplitudes and damping factors, etc.) with time-varying amplitudes and frequencies based on sliding window FFT. First, windows and interpolation are used to reduce spectral leakage and fence effect, and decrease the FFT identification errors. Then, through the sliding of the time window, the signal intercepted by each time window is transformed to obtain a dynamic sequence of oscillation frequency and oscillation amplitude, that is, varying frequency and amplitude with time. The dynamic sequence of the damping factor is obtained by analyzing and calculating the time-varying oscillation amplitude. Finally, using the ideal non-stationary signal and the measured signal of the power grid as test case, the comparison results with the Prony and HHT algorithms show that this method not only can eliminate the mode mixing, but also have anti-noise ability. The method can effectively identify the random time-varying oscillation modals and realize on-line modal onitoring and analysis of subsynchronous oscillation modals.

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