Theoretical Examination of Small-Signal Impedance Models of Inverter-Based Resources

Various impedance modeling methods have been developed in different reference frames for the impedance-based stability assessment (IBSA) of inverter-based resources (IBRs). In practice, these impedance models are extracted by applying electromagnetic transient (EMT)-type impedance scanning techniques to manufacturer specific (black-box) models of IBRs. However, the relationships between these models require a clearer and more comprehensible explanation. This work derives and systematically explains model equivalence through linear and coordinate transformations, as well as model simplification in the sequence multi-input multi-output (MIMO) to sequence singleinput single-output (SISO) impedance transformation. To validate the theoretical analysis, EMT-type impedance scanning is performed on a full-size converter (FSC)-based wind park (WP) in a benchmark test system exhibiting weak grid issues.