Analysis of Sub-synchronous Oscillation of Direct-drive Wind Farm Series Compensated Line with Prony Method

In this paper, the mechanism and characteristics of sub-synchronous oscillation of series compensated lines in direct-drive wind farms are studied based on the Prony method. For this purpose, a theoretical analysis is first conducted to reveal a relationship between the size of the transmission line series-complement capacitance and the parameters of the direct-drive wind farms network-side inner-loop controller and the system oscillation unstable. Moreover, a simplified series compensated lines model of the direct-drive wind farm is established to analyze the oscillation mode of sub-synchronous oscillation instability. Then, the Prony method is employed to identify the generated voltage signals, by which one can deduce that the direct-driven wind farm and the series compensated transmission line would cause a negative-resistance effect, leading to sub-synchronous oscillation instability. Finally, a comparative numerical simulation is carried out to demonstrate the efficiency of the proposed method.