Transient stability modes of DFIG in large disturbance based on reduced-order DAE models

Compared to conventional synchronous generators, large-scale renewable energy generations such as doubly-fed induction generator (DFIG) are coupled with the grid through power electronic (PE) interfaces. The new integrating pattern changes transient stability modes and brings new risks for operation of the grid. Yet the time scale-based modeling hierarchy is still heuristic, and thus make the stability mode theory ambiguous. In this paper, the reduced-order differential-algebraic equation (DAE) model is proposed based on the multiple-time-scale analysis of DFIG and singular perturbation equivalence method. It is proved that, as long as the PE interface works in the power-modulation scheme, DFIG's transient stability problem is mainly due to the fact that its simultaneous active power or active current surges to transmission limits of the network (network constraint approaches singularity), whereas the kinetic stability mode is difficult to observe in real application during large disturbances. The proposed stability modes are verified in case study by uncontrollable divergence of terminal voltages and currents.