Impedance Measurement

NREL has the hardware and software capabilities to assess with high detail how renewable energy devices will affect grid stability and strength.

NREL researchers work with the Flex manufactured battery enclosure.
Photo by Dennis Schroeder, NREL

As renewable energy and power electronics proliferate on the grid, it is critical to understand how these devices will affect grid stability. But there are far too many devices and commercial varieties to assess each device analytically and individually. Instead, the industry needs a versatile and tech-agnostic approach to determine device impacts quickly and confidently.

NREL has a software tool to perform impedance scans of devices, which evaluate how renewable energy resources interact with one another and the grid at multiple timescales and for various operations. This software is compatible with any renewable energy device and can prevent early mistakes in project planning.

For renewable energy deployments that require more rigorous field validation, NREL can also plug devices into its Advanced Research on Integrated Energy Systems (ARIES) platform, which has the ability to deliver real power for custom grid scenarios and analyze the devices’ electrical response.

Illustration of the United States showing the Flexible and Scalable Grid Impedance Scan Tool (GIST) for stability analysis on wind plants, PV plants, Storage, and Feeder with DERs all using GIST before going onto the grid.
Illustration by Taylor Henry, NREL


  • Grid Impedance Scan Tool
    NREL has developed the Grid Impedance Scan Tool (GIST), software to scan the impedance of any inverter-based resource (IBR), such as offshore and land-based wind power plants, solar power plants, battery energy storage systems, and high-voltage DC converter stations. GIST can scan the impedance of all types of device models (e.g., black-box, real code, and generic electromagnetic transient models) to evaluate their impact on grid stability and does not require analytical models of devices. It can be used to estimate the grid-forming capacity required or assess the stability impact of various control modes for devices.

  • Impedance Measurement System
    NREL has developed an in-house hardware testing system to measure impedance responses of multi-megawatt wind turbines and solar and battery inverters for characterizing their stability properties at different frequencies. The system is being used by several Department of Energy- and industry-sponsored projects to evaluate the stability impacts of wind turbine and inverter products.

  • Medium voltage impedance network
    This hardware unit can simulate impedance conditions to test device-grid interactions under widely diverse scenarios, including weak grid conditions and series-compensated transmission lines.

  • Controllable grid interface
    This hardware unit customizes power conditions for a 19-MW research bus.


Impedance Scan Tools for Stability Analysis of IBR Grids, G-PST/ESIG Webinar Series (2022)

Which IBRs Are Causing Oscillations? – A Flexible and Scalable Impedance Scan Tool To Evaluate Small-Signal Stability, Control Interactions, and Oscillations in IBR Grids, NERC Inverter-Based Resource Performance Working Group (2021)

Control System Stability for Converter-Dominated Grids, Energy Systems Integration Group (2020)

Impedance of Three-Phase Systems in DQ, Sequence, and Phasor Domains, IEEE Power and Energy Society (2020)


Real-World 20-Hz IBR Subsynchronous Oscillations: Signatures and Mechanism Analysis, IEEE Transactions on Power Systems (2023)

Real-World Subsynchronous Oscillations Events in Power Grids With High Penetrations of Inverter-Based Resources, IEEE Transactions on Power Systems (2022)

Reversed Impedance-Based Stability Criterion for IBR Grids, 21st Wind and Solar Integration Workshop, The Hague, Netherlands (2022)

Sequence Impedance Measurement of Utility-Scale Wind Turbines and Inverters – Reference Frame, Frequency Coupling, and MIMO/SISO Forms, IEEE Transactions on Energy Conversion (2022)

Impedance Methods for Analyzing Stability Impacts of Inverter-Based Resources: Stability Analysis Tools for Modern Power Systems, IEEE Electrification Magazine (2021)

Control, Operation, and Stability Characteristics of Grid-Forming Type III Wind Turbines, 19th Wind Integration Workshop (2020)

Impedance-Based Prediction of Distortions Generated by Resonance in Grid-Connected Converters, IEEE Transactions on Energy Conversion (2019)

Impedance Measurement of Wind Turbines Using a Multimegawatt Grid Simulator, 18th Wind Integration Workshop (2019)

Large-Signal Impedance-Based Modeling and Mitigation of Resonance of Converter-Grid Systems,” IEEE Transactions on Sustainable Energy (2019)



Shahil Shah

Senior Power Systems Engineer