In 2021, the U.S. set a goal to reduce greenhouse gas emissions 50% below 2005 levels by 2030 and achieve economy-wide net-zero emissions by 2050. Meeting these goals involve increased deployment of “inverter interfaced energy resources,” such as solar, wind, and battery storage systems. Energy companies are actively working on ways to maintain the reliability, security, and resiliency of transmission and distribution systems with this anticipated increase.
Historically, inverters have relied on the grid for the voltage necessary to sustain electricity. However, when grid disturbances occur, these inverters either provide minimal grid support or cause a disconnection from the grid. Such reactions can potentially reduce needed reliability and resiliency.
A new fleet of inverter technology is under development known as “grid forming inverters.” These can improve grid stability in regions with higher penetration of inverter-based resources. They can support greater use of renewable energy in small, isolated grids, or microgrids. They can also help sustain and black start a grid if a power system experiences a partial or total shutdown.
Through a Department of Energy-funded project led by the University of Washington, and through a UNIFI consortium co-led by National Renewable Energy Lab (NREL), EPRI, and the University of Texas at Austin, collaborators have developed a generic grid forming inverter simulation model. Since its first iteration, EPRI has improved the model, recently updating information regarding model set up, , its control system architecture, and values of parameters used to configure the model, among other details.
Using this model, system planners can determine performance requirements of inverter-based resources that can be beneficial for their specific footprints. They also can evaluate where grid upgrades may be needed and analyze the impact of those requirements on grid operation.
This model can be especially useful for energy companies needing to perform a system study prior to an interconnection request. For example, developers may submit a solar power project for interconnection, but the energy provider does not know which solar company will construct the plant or what kind of inverters they will use. The energy provider can still move forward with an initial exploratory system study using this model, whether it is a transmission, distribution, or microgrid study. Planners also can include detailed performance requirements when using the model to develop request for proposals for inverter-based power plants.
System operators can apply this model in transmission, distribution, and microgrid studies to analyze the impact of grid forming inverters, and this model continues to evolve, EPRI encourages additional testing and validation of the model to determine its limitations and incorporate further improvements from users.
The model is free and publicly available from PSCAD’s knowledge base. Users also can find specifications of the model in the recent EPRI update Performance Requirements for Grid Forming Inverter Based Power Plant in Microgrid Applications: Second Edition. In addition, EPRI has the model available in a variety of simulation software platforms.