Models and Method for Short-Circuit Analysis in the Presence of Inverter-Based Resources

Modern power systems are transitioning from traditional synchronous generators to inverter-based resources (IBRs). Unlike synchronous generators, which behave as linear Thevenin sources, IBRs exhibit nonlinear, control-dependent fault responses. Existing short-circuit analysis methods often rely on simplistic tabular models or proprietary control parameters that are not scalable or system-agnostic. This paper aims to provide a robust, scalable, and system-agnostic framework for short-circuit analysis in IBR-rich power systems.

The authors introduce two primary modeling advancements. First, they propose an equation-based model for grid-forming (GFM) inverters that emulates the constant voltage source behavior of synchronous generators during faults, eliminating the need for proprietary filter parameters. Second, they utilize a machine learning (ML) approach—specifically a decision tree algorithm—to model Type III wind turbine generators (WTGs) in compliance with the IEEE 2800-2022 standard. This ML model learns the relationship between terminal voltage drops and current injections, making it system-agnostic and highly accurate.

The paper improves the existing phasor domain short-circuit analysis (PDSCA) framework by introducing a voltage superposition-based approach. This method separates the system into linear and nonlinear components, allowing for an iterative solution that accounts for both positive and negative sequence current injections. To address convergence issues common in IBR-dominated systems, the authors implement an adaptive weighted change-limiting algorithm combined with negative sequence current averaging. This framework was validated on the IEEE 39-bus system with 84% IBR penetration, demonstrating high accuracy and computational efficiency.

This research provides a practical, non-proprietary method for utilities to perform short-circuit studies in systems with high renewable penetration. By generating accurate network equivalents at the point of interconnection, the proposed method allows utilities to share system information with neighboring operators without requiring complex electromagnetic transient (EMT) simulations, which are often computationally expensive and inaccessible to many utilities.