The wind power grid connected system relies on a phase-locked loop to maintain synchronous operation with the system and achieve decoupling control of active and reactive power.Under large disturbances

the phase-locked loop is highly susceptible to the influence of the grid connection point voltage

leading to wind turbines losing synchronization and disconnecting from the grid.Firstly

the equivalent rotor motion equation of the direct driven wind power grid connected system during the transient period was established

and its synchronization characteristics were characterized and analyzed.Then

by analogy with the power angle stability theory of traditional synchronous generators

analyze the existence of the transient stability equilibrium point of the system under a certain initial state and fault intensity.On this basis

the transient stability domain of active and reactive current injection during power grid faults was comprehensively characterized

and a series of characteristic points in the stability domain were analyzed in detail

providing design basis for different purpose oriented stability control strategies.Finally

a simulation model of a direct driven wind power grid connected system was built on the PSCAD platform

and the transient characteristics of the system under active and reactive current injection at corresponding feature points were quantitatively analyzed.Relevant simulation cases verified the theoretical analysis and the rationality of the proposed transient stability domain.