Researchers at Oak Ridge National Laboratory, or ORNL, in Tennessee are exploring a new type of power system modeling known as electromagnetic transient, or EMT, domain analysis, that may be key to addressing inverter-based resource faults and integrating more distributed resources into the evolving grid.
The North American Electric Reliability Corp. in March issued an alert and recommendations to solar generators following a series of disruptions to inverter-based resources. The reliability organization has tracked a growing number of instances where inverter-based resources tripped offline or reduced output in response to geographically-distant grid disturbances.
NERC also issued reliability guidance noting EMT “simulations are necessary to adequately identify and mitigate [bulk power system] reliability risks moving forward.”
ORNL researchers say compared with traditional modeling, EMT analysis can give grid operators a more accurate understanding of rapidly-unfolding grid events. System planning and management has become more complicated as new types of electric power equipment are connected to the grid, including solar and wind plants, electric vehicle chargers, and washers and dryers with variable frequencies, according to Suman Debnath, a researcher at the lab.
This grid evolution requires a move “away from the traditional analysis tools that were being utilized for planning interconnection studies,” Debnath said in an interview. “There will be a need to move towards using [EMT] simulations, which require a smaller time steps and which require more fidelity.”
“There are definitely challenges with performing EMT simulations,” Debnath added, including understanding how to validate new models and scale analysis up from individual inverters to regional grids. “That is the crux of the research that we are doing here.”
Working with Southern California Edison, the lab integrated new models and algorithms into an EMT domain analysis tool and earlier this year was able to replicate a 2018 transmission fault that caused a large solar plant to reduce output to the utility’s system.
“Developing a high-fidelity model will help utilities better understand the physical dynamics of the power electronics, thus improving grid performance and aligning with our future vision of grid modernization,” Md Arifujjaman, senior engineer for grid technology innovation at Southern California Edison, said in a statement.
ORNL will host a workshop on Aug. 24 and 25 in Knoxville, Tennessee, in collaboration with the Department of Energy and NERC, to share its research on the fault replication and how EMT modeling can be used for planning and interconnection studies.
“There will have to be resource upgrades that can happen on the power grid side, and there could be certain upgrades that can happen within the plant itself,” Debnath said. A combination of those two could have prevented the fault ORNL and Southern California Edison were able to replicate through modeling.
“Some utilities and system operators are at this point embracing electromagnetic transient simulation,” Debnath said. The upcoming event will allow ORNL to share its research and host a discussion on challenges that grid stakeholders may be facing in utilizing the more complex analysis.
The lab’s work on the topic will continue for years, he added.
“I think one of the things that we’re continuing to work on is understand how to look at improving the modeling capabilities in this domain, and how to improve the ability to scale the analysis,” Debnath said.