Bifurcation behavior of wind energy generation systems

Use of the doubly fed induction generator (DFIG) in wind energy generation systems allows variable speed operation by using partially rated back-to-back PWMconverters. Although many control schemes have been reported in the literature to address some specific control problems, few has considered the general stability of the entire system. Specifically, bifurcation analysis of the system has not been reported so far. Lowfrequency oscillation has been found in a practical power grid system with the wind farm being connected to single-phase constant power loads. In this paper, the rotor speed of the DFIG is used as a variation parameter for bifurcation analysis. Bifurcation diagram of the voltage link capacitor clearly indicates the instability phenomenon of the practical DFIG system in supersynchronous operation when unbalanced single-phase constant power loads are connected to the connecting grid.