Dynamic stability is a major concern in maintaining the security of power grids with high shares of power electronics-based resources. Stability analysis tools are needed to evaluate the impacts of power electronics converters on system stability at slow and fast time scales. This project will investigate a new impedance scan method, which provides a more accurate impedance representation to investigate stability challenges associated with power electronics connections. If the project is successful, it will enable power engineers to do similar studies in the future and obtain a more accurate impedance representation.
Benefits
The net benefits for consumers from this project is expected to be delivered collectively from lower cost and risk for power electronic based devices connections, i.e. wind farm, solar farm and HVDC connections.
The outputs of this research will support energy networks building more understanding on interaction and instability issues associated with power electronics converters. It will allow the better planning for integration of power electronic devices. It will also help us in taking mitigating actions to avoid unplanned outages resulting from interaction issues.
Learnings
Outcomes
An impedance scan tool is developed for the analysis of subsynchronous, near-synchronous, and super-synchronous control interactions in power electronics interconnections. The tool is implemented in PSCAD and Python, with a graphical user interface and comprehensive user manual.
Developed the stability criteria suitable for the investigated impedance scan method to evaluate the stability impacts of power electronic devices. Impedance characteristics of power-electronic converters, impedance interactions between the converters and the system were analysed, stability criteria were documented and comprehensively identified the oscillation frequency in subsynchronous, near-synchronous, and super-synchronous ranges.
The developed scan tool is validated with different application scenarios, with an evaluation report on the impact of power-electronic interconnections on system oscillation modes and control interactions. HVDC interconnection to the AC grid was screened for oscillation risks. The tool is used to analyse a selected GB network area under agreed current and future scenarios to evaluate stability risks, and the findings are validated through time domain studies in PSCAD.
Materials were developed for a two-day training workshop, including fundamental information on impedance-based stability analysis, characteristics of the power-electronic converters and their interaction with the grid, guidance on the scan tool interface, and practical scan settings (such as injection type and perturbation magnitude). Demo projects are developed to provide training from step-by-step setup of the scan tool to hands-on practice of impedance scans and stability studies.
Lessons Learnt
2023/2024
The integration of power-electronic converters has modified the impedance performance of power systems. Traditional impedance performance relies on the single-dimensional RLC (resistor-inductor-capacitor) representation, whereas converters introduce a two-dimensional impedance matrix performance due to the mirror frequency coupling effect of converter control. This results in the oscillation induced by converter control exhibiting two frequencies at mirror frequency positions.
In future projects related to oscillation analysis of power-electronic power systems, multiple-frequency oscillations need to be taken into consideration.
2024/2025
The project compared both the dq impedance scanning method and the dq sequence impedance method for the impedance analysis. It was shown that both methods are equivalent in terms of stability analysis. It should be noted that the term "sequence" here refers to components in the dq frame, not the traditional sequence components of the abc system.
The project aims to disseminate learnings to a wider group of stakeholders and provide training to relevant NGET personnel and external stakeholders. It’d be useful to plan this well ahead with the wider industry stakeholder group before completing all the study works required for the project. This will ensure the efficiency and smooth delivery of the knowledge transfer workshop.
2025/2026
The project has been completed. It is recommended that sufficient resource is allocated for ongoing updates and validation, so that the tools remain effective under changing network conditions and future power-electronics developments.
Dissemination
2023/2024
A workshop on the 'Impedance Scan Project' was held at National Grid on 19th March 2024, to disseminate the effectiveness of the developed impedance scan tool. The automation feature for the scanning process with this tool was demonstrated.
2024/2025
An online workshop has been held on 24 March 2025 for demonstrating the developed impedance scan tool. Dissemination workshops are planned to be held in early July.
2025/2026
A two-day workshop was held at National Grid on 2-3 July 2025. On day 1, impedance-based stability analysis, mechanism of control interaction between the power-electronic converter and the network, and the developed impedance scan tool were introduced. Day 2 was a hands-on practice session where users worked with provided demo projects, setup the tool and simulation models for scan, and performed stability analysis using the developed scripts.
