Short-Circuit Blackbox Modeling of Inverter-Based Resources: Lessons Learned

The fault response characteristics of synchronous generators are inherently governed by their physical attributes and construction. In contrast, the fault response traits of Inverter-Based Resources (IBRs) are intricately tied to their vendor-specific control schemes and settings. In the last decade, generic IBR models have been developed for short circuit studies by different power system analysis software vendors. IEEE PES-TR78, published in 2020, reports another approach of using tabular data to model fault repose of IBRs. As will become clear in this paper, this approach has its own limitations and challenges. Recently, like the common practice in transient studies, (Dynamic Linked Library) DLL black-box modeling has been proposed for steady-state short circuit analysis.

In this paper, the Electro Magnetic Transient (EMT) models of inverters, obtained from three distinct vendors, are investigated. Following a comprehensive analysis of the fault responses, a vendor-specific Blackbox DLL is developed for each vendor's inverter. These DLLs are meticulously validated for accuracy by comparing their output against the results obtained from the EMT simulation. Throughout the development of the DLLs, valuable insights into the varying approaches taken by different vendors to respond during fault conditions will be gained and shared.

The exploration in this paper focuses on several critical aspects, including the implementation of Voltage Ride-Through (VRT) detection logic by each vendor, the distinctive characteristics and shapes of VRT curves, and whether hysteresis feature is employed by various vendors under the condition of voltage toggling during remote faults. Furthermore, we present the differences in positive and negative sequence current injection logic among vendors, their approaches to control logic for angle rotation in scenarios involving close-in three-phase faults, and how they manage the curtailment of positive and negative sequence currents when current limits are reached during unbalanced faults. This work not only advances our understanding of IBR dynamics but also lays the groundwork for more robust and reliable power system analysis in the context of modern electrical grids.