To meet the needs of energy transition to renewables, and address the challenges posed by declining system inertia and strength, a significant number of converters with grid forming capabilities will be necessary to ensure future power grid security. This project seeks to tackle the complexity arising from the various models, configurations, and control modes of grid forming converters by developing generic converter models. The project will also aim to assess and identify any potential instability risks associated with deploying grid forming converters and develop mitigation measures to address any identified risks.
Benefits
This project will contribute to reducing instability risk for future network and thus will have a positive impact on cost savings to consumers.
Learnings
Outcomes
Outcome 1 – Literature review and foundation for further work
A literature review on grid-forming converters was completed and delivered as Deliverable 1. This deliverable provides a comprehensive review of grid-forming control, converter-related power system stability, stability analysis methods and converter modelling. It established a foundation for the subsequent work on modelling and stability analysis of grid-forming converters
Outcome 2 – Development and validation of a generic grid-forming converter model
A generic model incorporating four types of control strategies, supporting inertia and islanded operation, was developed and is available in both PSCAD and PowerFactory (DIgSILENT). Two of the control strategies also offer black-start capability. The developed generic model aligns with grid requirements and is adaptable to applications including High Voltage Direct Current (HVDC) systems, wind turbines, energy storage and STATCOMs. The developed generic models were also validated via Real Time Digital Simulators, and performance assessment on grid-forming capability was completed against Grid Code
Outcome 3 – Stability analysis and stability improvement methods
The influence of key parameters such as virtual inertia, damping and line impedance on system stability was examined through small-signal and transient analysis approaches. The effect of control parameters, especially inertia, on both small-signal and transient stability was identified. Stability improvement methods were presented and validated. The report states that transient stability performance can be improved by tuning the controller parameters, using a compensator to adjust the given references, or regulating the maximum current vector. The stability enhancement strategies were incorporated into the generic model, with a user interface developed to facilitate configuration
Final TRL achieved: TRL 5
Further exploitation of the project outputs would support progression to the next TRL through broader validation of grid-forming converter performance in more complex and large-scale system scenarios, together with continued refinement of the generic model and user interface for practical engineering use. These activities would strengthen confidence in robustness, scalability and applicability in more representative network environments, enabling progression beyond the current simulation and pilot-scale validation stage.
Total NIA Expenditure on project
External Cost £468,290
Internal Cost £110,158
Total cost £578,448
Lessons Learnt
Multiple Control Strategies for Grid-Forming Functionality: Many converter control strategies can perform certain functions associated with grid-forming capabilities. It was found that even a current-source-based control can support islanded operation. A generic grid-forming converter model incorporating four types of control strategies was developed for this functionality.
Droop Control and ROCOF Relationship: The mechanical inertia of a synchronous generator, in mathematical terms, is equivalent to a low-pass filter in droop control. This explains how the Rate of Change of Frequency (ROCOF) is maintained as system dynamics are slowed.
Interaction Between Converter Parameters and Grid Strength: Stability of GFM converters was shown to be fundamentally determined by the interaction between virtual inertia, damping, current-limiting behaviour and grid strength. Increasing virtual inertia and damping can improve transient stability, extend critical clearing time and enhance frequency support, while excessive or mismatched inertia may introduce transient angle instability in weak grids or poorly damped oscillations in strong grids.
Current Limitation as a Stability Control Mechanism: Current limitation was shown to be not only a protection function but also a key stability control mechanism. Both the magnitude and phase angle of the current vector significantly affect the decelerating area and post-fault recovery capability.
LVRT Compensation and Stability Assessment Methods: LVRT compensation effectively enhances fault ride-through performance and maintains synchronism under severe disturbances. By combining phase-portrait transient analysis with state-space small-signal modelling, the work established a framework for assessing GFM stability under realistic operating constraints, including current saturation and varying grid inertia.
Relevance to PLL-Based Grid-Supporting Converters: The findings indicate that PLL-based grid-supporting converters can be interpreted within a similar swing-equation framework. Comparable stability enhancement approaches can therefore be applied through current reference adjustment and virtual inertia/damping control.
Dissemination
Dissemination will be arranged once the project is completed via workshop and publications of journals or conference papers. A journal paper is planned to submit in summer to disseminate some of the key project findings and outcomes.
