Large-Signal Modeling of Virtual Admittance-Based Grid-Forming Inverter

As wind power capacities increase, the decreasing inertia of modern power systems challenges its frequency stability. Unlike traditional grid-following inverters, grid-forming (GFM) inverters can create and stabilize a grid independent of the utility. Hence, GFM inverters are seen as a potential solution, but their transient stability is a growing concern. While large-signal models are effective tools for analyzing transient stability, most existing research focuses on typical GFM control schemes without using virtual impedance. To address such a research gap, this paper proposes several simplified large-signal models for GFM inverters with virtual admittance, showing that the second-order model closely matches the accuracy of the full-order EMT model. So, the second-order large-signal model is a competing candidate for transient stability analysis due to its simplicity and accuracy. Finally, the correctness of the proposed models has been verified by time-domain simulations.