Z-tool: Open-Source Frequency-Domain Analysis Toolbox for EMT Models

Etch - The Energy Transmission Competence Hub - have released an open-source Python-based implementation for the stability analysis of AC/DC power systems.

The PSCAD-based tool is available to download free here

The core functionalities are impedance/admittance characterization and small-signal stability assessment. The analysis relies on an existing system model in the EMT simulation software PSCAD.

The following features are currently implemented and validated:

• Voltage perturbation-based admittance scan at several nodes, including MMC-based systems and black-box components
• Stability assessment via Generalized Nyquist Criteria applicable to standalone-stable MIMO systems
• Oscillation mode identification via eigenvalue decomposition (EVD) and bus participation factors
• Passivity assessment and Singular Value Decomposition functions

The flowchart below summarizes a common usage of the tool for stability studies, including frequency-domain system identification (frequency_sweep) and several stability analysis functions (stability_analysis):