FAST-Enabled Controller-Parameter-Parameterized Immittance Transfer Function for Retuning Black-Boxed Inverter-Based Resources

Abstract

Frequency-domain passivity analysis enables stability screening of black-boxed inverter-based resources (IBRs) directly from measured immittance; however, industrial retuning is often constrained by the lack of a direct mapping from stability-margin targets to controller settings. This letter presents a controller-parameter-parameterized immittance transfer function (CPP-ITF) that represents each immittance element as a rational function whose coefficients are explicit polynomials of a selected tuning parameter. Using a small design-of-experiments (DOE) set (i.e., frequency scans at a few parameter values), the CPP-ITF is identified per frequency and combined with a measured grid-impedance profile to evaluate stability margins over dense parameter grids without additional EMT simulations or scans. Implemented in AEMO’s in-house Frequency-domain Admittance-based Stability Tool (FAST) and operationalized via a four-step workflow, the method provides directional tuning guidance and auditable feasibility windows over stability-risk bands. A case study demonstrates accurate prediction of sequencedomain impedance versus the selected tuning parameter, scanfree margin screening across multiple SCRs, and EMT validation at the predicted SCR-dependent critical limits.