A Python Based Automatic Impedance Scan Tool for PSCAD Models

The growth of inverter-based resources (IBRs) in power systems leads to stability challenges on system operations that were not of major concerns in the past, such as control interactions among IBRs and between IBRs and other components within the transmission network. Control instability for the IBRs operating under weak grid conditions and sub-synchronous control interaction (SSCI) for IBRs connected near series compensated transmission lines are common phenomena considered by system operators. Electromagnetic transient (EMT) study incorporating high bandwidth EMT models are required to assess weak grid control interactions and SSCI issues because positive-sequence electromechanical dynamic models are generally considered inadequate for these types of studies. However, EMT studies are more time-consuming and demand more computational resources. In practice, an SSCI screening process is adopted by system operators during the interconnection process to shortlist the potential vulnerable IBRs for further assessment using detailed EMT simulations. A frequency domain analytical approach is emerging within industry research communities in recent years to evaluate the stability of an IBR dominated system. The impedance characteristic profiles of the IBRs are necessary to use a frequency domain study approach. A python-based impedance scan tool applicable to the PSCAD models has been developed at ERCOT to automatically conduct the frequency scan process. Considering the frequency-coupling effect, the developed toolset, namely ZSC, scans the IBR's impedance based on individual frequency perturbation signals and the tool has been incorporated into the PsCad Auto Run (PCAR) platform developed at ERCOT. This paper presents the schematic of the ZSC tool and some implementation notes on selected PSCAD models.