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Interaction between doubly fed induction generator (DFIG) Type 3 wind generators and series-compensated networks can lead to subsynchronous resonance (SSR) oscillations-a phenomenon observed in the real world. In this paper, impedance-based Nyquist stability criterion is applied to analyze the SSR phenomena. Impedance models of a DFIG along with its rotor-side converter (RSC) and grid-side converter, and a series-compensated network are derived in terms of space vectors. The DFIG impedance and the network impedance are analyzed to show the impact of wind speed, compensation level, and RSC current controller gain on SSR stability. Nyquist maps are also used to demonstrate the impact on SSR stability. Simulation studies are carried out to show SSR controller interaction. This paper successfully demonstrates that the interaction between the electric network and the converter controller is a leading cause of the SSR phenomena recently observed in wind generation grid integration.
Date of Publication: Dec. 2012