Nonlinear Analysis of SSR in Wind Power Plants

This paper analyzes sub-synchronous resonance (SSR) in future wind power plants (WPPs) using bifurcation theory, a nonlinear analysis approach. SSR, and in particular the Induction Generator Effect (IGE) is likely to occur more frequently as large amounts of wind power are incorporated into power networks, supported by series compensation to improve power transfer capability. A nonlinear 10^th order modified IEEE first benchmark model is developed. Bifurcation analysis reveals the critical conditions resulting in IGE are identified as a Hopf bifurcation point, verified by considering the trajectory of system eigenvalues and also through transient time domain simulation. The application of bifurcation theory is compared with the linear Nyquist stability criterion. The results from the Nyquist approach show that both analytical methods are in agreement with each other. However, the nonlinear bifurcation analysis determines system stability with respect to any parameters of interest, whereas the Nyquist stability criterion only determines the system stability at a specific operating point.