Modeling of DFIG-Based WTs for Small-Signal Stability Analysis in DVC Timescale in Power Electronized Power Systems

This paper presents a dynamic modeling methodology of a DFIG-based wind turbine (WT) for small-signal stability analysis in DC-link voltage control (DVC) timescale in power electronized power systems. The DVC timescale (around 100 ms) is determined by DVC, terminal voltage control, active power control, and phase-locked loop in DFIG WT. Motion equation concept is introduced and extended to describe DFIG WT external characteristics in the concerned timescale. The relation between the active/reactive power imbalances and phase/magnitude dynamics of defined synthetic internal voltage (inner potential) vector are developed. The model in DVC timescale is similar to synchronous generator rotor motion equation that is in electromechanical timescale (around 1 s) and familiar to power engineers. With the developed model, characteristics of equivalent inertia, damping and synchronizing coefficients of DFIG WT in DVC timescale can be understood, and the dynamic interactions among multiple DFIG WTs, as well as between DFIG WT and other grid-connected devices in DVC timescale can be fully interpreted. Comparisons of eigenvalues show that the proposed model can hold the main behaviors of concern. Applications on the stability analyses of DFIG WT inter-connected with VSC-HVDC system and two-DFIG WT system are taken as examples to validate the feasibility of the proposed model.