Impedance Modeling of Virtual Synchronous Control of Doubly-Fed Wind Power System Under Weak Grid Condition

Stability problem on doubly fed induction generator (DFIG) based wind generation systems could be obvious under the connected weak grid, though the virtual synchronous control (VSC) based DFIG could provide frequency support for the weak grid and improve the stability of the grid connection, the stability analysis is insufficient. Aiming at the grid-connected stability analysis of the VSC based DFIG, this paper proposed the output impedance modeling in dq rotating coordinate system and analyzed the stability effects. Firstly, the impedance model of DFIG with the VSC is derived by using the small disturbance analysis method. Secondly, the output impedance characteristics are obtained and validated by model-based frequency scanning method. Finally, the influence of different grid strengths and the VSC parameters on the stability is analyzed by using the generalized Nyquist criterion (GNC). The results show the derived output impedance models are valid, and the stability of DFIG using the VSC could be effected by the virtual inertia time constant and virtual damping coefficient.