Coupling characteristic of DFIG-based WT considering reactive power control and its impact on phase/amplitude transients stability in rotor speed control timescale

Abstract

The transient stability issues caused by doubly fed induction generator (DFIG)-based wind turbine (WT) itself are received increasing attentions. The q-axis reactive power control (QCtrl), as an essential part of DFIG-based WT, has a significant effect on its transient response. In this paper, the impact of QCtrl on the phase/amplitude transient stability of DFIG-based WT-dominated system is analyzed from the perspective of internal voltage amplitude-phase coupling characteristic. Firstly, an amplitude/phase dynamic model of DFIG-based WT in rotor speed control timescale (about seconds, corresponding to traditional electromechanical timescale) is developed. Then, in comparison with familiar synchronous generator (SG), an inherently amplitude-phase characteristic of internal voltage of DFIG-based WT is identified. Next, taking the DFIG-based WT-dominated system as an example, the impact of QCtrl on system transient stability via the internal coupling paths is analyzed. A novel phase-amplitude coupling instability mechanism is found, which is different from that in traditional SG-dominated system. Finally, the effects of different QCtrl strategies on transient stability are discussed.