Impedance network-based oscillatory stability analyzer (INOSA) - A frequency domain tool for investigating IBR-grid interactions

Unstable subsynchronous oscillations (SSOs) may be excited due to adverse interactions between inverter-based resources (IBRs) and series-compensated or weak ac networks. The frequency-sweep impedance modeling and analysis method is widely used for scanning grid-tied IBRs against the risk of SSO. The stability of such a system is heavily influenced by system-wide parameters such as IBR dispatching conditions (input resource, and different dispatch scenarios), and network status (short-circuit and/or series-compensation levels). The variation in the operating conditions must be taken into account when conducting frequency-scanned impedance-based modeling and analysis. This paper proposes a tool, named impedance network-based oscillatory stability analyzer (INOSA), which integrates decades of research on impedance-based analysis to investigate the risk of SSO under varying operating conditions. The INOSA tool is developed as a MATLAB application package. It takes the available system parameters and frequency-scanned impedance data as input and processes it to carry out impedance network-based stability analysis under all operating conditions. The developed tool outputs key stability information such as damping and frequency of each oscillation mode, and a multi-dimensional security boundary/region plot that can be used to assess the risk of SSO and take appropriate measures. A case study on an actual power system is presented to demonstrate the features and capability of the analysis tool.