Grid-forming wind turbine is an important equipment in improving the frequency stability of new energy power systems. However

the coupling between active and reactive power in grid-forming wind turbine reduces its support capability. In order to analyze the influence of grid-forming impedance ratio on the power coupling characteristics of the grid-forming wind turbine

a small signal model of grid-forming wind turbine considering power coupling characteristics is set up in this paper

the system stability margin is determined by using the Nyquist stability criterion

and the influence of impedance ratio variation on system dynamic characteristics is analyzed. The study shows that when the grid impedance ratio of the grid-forming wind turbine decreases

its power coupling shows nonlinear and deepening trend

causing oscillations in the transient process to diverge and eventually leading to turbine instability. The feasibility and correctness of the theoretical analysis in this paper have been verified by both simulation and experimental results.