Nonlinear Stability Assessment of Type-4 Wind Turbines During Unbalanced Grid Faults Based on Reduced-Order Model

As the number of converter-based renewable generations in the power system is increasing, the inertia provided by the synchronous generators is reducing, which in turn is reducing the stability margins of the power system. In order to assess the large-signal stability, it is essential to model the wind power plant connections accurately. However, the actual EMT models are often unavailable, black-boxed, or computationally too heavy to model in detail. Hence, simplified reduced-order models (ROMs) resembling the actual system behaviour have gained prominence in stability studies. In this regard, an improved WT ROM was proposed to investigate large signal stability during unbalanced grid faults. The methodology presents a systematic way to model the coupled sequence components of the WT ROM for various grid faults. Based on the studies carried out in this paper, it is observed that post unbalanced grid disturbances the proposed WT ROM correctly tracks the angle and frequency, and its trajectory is a good match when compared to a detailed simulation model in PSCAD.