Currently vendors are obliged to provide NESO encrypted ‘black-box’ simulation models of inverter-based resources (IBRs). However, there isn’t an easy way to use these black-box IBR models to form a state-space model of the IBR-dominated power grid for analysing sub-synchronous oscillations (SSO). Use of the white-box generic IBR models is an option but proper parametrisation of these across a range of operating conditions remains a challenge.
This project will use a digital twin (DT) of IBRs with its parameters estimated based on perturbed data from high-fidelity real-time simulation. The parameterised IBR models in conjunction with the known dynamic model of the rest of the grid (including synchronous machines, loads etc.) would form the overall state-space model for studying SSO under different operating conditions.
Benefits
A digital twin-based stability analysis tool will enable NESO to parameterise IBR models, study SSO, and identify root cause using conventional modal analysis systematically. Currently without well parameterised DTs of IBRs, developing a state-space model in a bottom-up way to study SSO is challenging, risking SSO events or forcing NESO to operate conservatively.
This project is expected to provide several benefits, including:
- Enhanced system security and reliability by reducing system risk and avoiding negative control interactions (ranging from small wobbles to extreme blackouts), allowing higher fractions of renewables (IBRs) without compromising the security of supply.
- Improved quality of supply and services.
- Lower bills for consumers by reducing the probability of downtime, brownouts or blackouts.
- Support for Net Zero goals.
Learnings
Outcomes
The project is currently in the early stages of WP1 and is progressing towards the development and validation of a digital twin-based small-signal stability analysis approach for IBR-dominated systems. At this stage, the main outcome is emerging technical evidence that the proposed bottom-up digital twin framework can capture the operating point dependence of IBR frequency response and support analysis of poorly damped sub-synchronous oscillations.Work undertaken to date has developed and tested a geometric method for representing the operating point dependence of inverter-based resource dynamics. Initial testing has been completed at both individual IBR level and on a modified IEEE 39-bus test system with high IBR penetration, with results indicating that the approach can estimate system frequency response and assist with identifying the potential root cause and geographical spread of SSO.
The project has not yet reached final delivery or full implementation stage. The WP1 report, which is due by the end of September 2026, will provide the formal evidence base for the parameter estimation approach and will further document the progress made against the project objectives and success criteria. The expected future outcome remains the development of a scalable stability analysis tool that can support quicker scenario screening, improved understanding of SSO risk, and more targeted identification of potential mitigation options once further validation and testing have been completed in later project stages.
Lessons Learnt
The project has highlighted the importance of validating the digital twin approach against detailed EMT models early in the project lifecycle, as this provides confidence that the proposed method is technically robust before wider application. Early testing on both individual IBR models and system-level test cases has helped confirm that the tool can capture operating point dependence and support root-cause analysis of poorly damped SSO.A key early learning point is the value of confirming which validation routes will provide sufficient confidence without adding unnecessary complexity. This is particularly relevant where different modelling environments or simulation platforms could be considered, as early agreement helps keep WP1 focused on the highest-value technical activity.The work to date also highlights the benefit of taking a structured, modular approach during the early development of the digital twin capability. This supports clearer testing of individual components before wider system-level application and helps identify any technical issues early in the project lifecycle.
For future projects, it would be beneficial to agree model availability, validation expectations, data requirements and computational considerations as early as possible. This should help reduce the need for later scope clarification and ensure that early work packages are set up to provide clear and usable evidence for subsequent project stages.
