The transient stability issues caused by doubly fed induction generator (DFIG)-based wind turbines (WTs) are receiving increasing attention. The q-axis reactive power control (QCtrl)

as an essential part of DFIG-based WTs

has a significant impact on its transient response. In this paper

the impact of QCtrl on the phase/amplitude transient stability of a DFIG-based WT-dominated system is analyzed from the perspective of internal voltage amplitude-phase coupling characteristics. First

an amplitude/phase dynamic model of a DFIG-based WT in rotor speed control timescale (in seconds

corresponding to traditional electromechanical timescale) is developed. Then

in comparison with familiar synchronous generators (SGs)

an inherently amplitude-phase characteristic of internal voltage for a 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 a traditional SG-dominated system. Finally

the effects of different QCtrl strategies on transient stability are discussed.