Integrating renewable energy sources like wind and solar into the nation’s power grid isn’t straightforward.
These sources generate direct current (DC), while the grid primarily operates on alternating current (AC).
The Role of Power Inverters
Power inverters are essential in this process. They utilize internal switches to convert DC into AC, enabling renewable resources to feed electricity into the grid.
As the U.S. increases its reliance on wind, solar, and battery storage, it’s imperative for utilities to grasp how these inverters will function within the grid’s complex infrastructure.
UNIFI Consortium’s Collaborative Effort
Researchers at the Pacific Northwest National Laboratory (PNNL), in collaboration with partners, have developed innovative models to assist power system engineers in evaluating the potential of grid-forming inverters – a new technology aimed at improving grid stability.
This effort is part of the Universal Interoperability for Grid-Forming Inverters Consortium (UNIFI), a $25 million initiative launched by the Department of Energy (DOE) in 2021. UNIFI brings together experts from academia, industry, utilities, and system operators to advance grid-forming inverter technologies.
First Industry-Approved Grid-Forming Inverter Models
The newly developed models, REGFM_A1 and REGFM_B1, created by PNNL in collaboration with inverter manufacturers, software providers, and power system planners, have recently received approval from the Western Electricity Coordinating Council (WECC), which oversees the western power grid.
This marks a significant milestone, as these models are the first industry-approved, publicly accessible grid-forming inverter models integrated into commonly used simulation tools like Siemens PSS®E and PowerWorld Simulator.
These models represent two prevalent grid-forming technologies: droop control and virtual synchronous machine control.
Enhancing Grid Stability with Grid-Forming Inverters
Wei Du, an electrical engineer at PNNL and lead developer of these models, emphasized their importance: “As renewable energy becomes a larger part of the energy mix, the power grid requires more grid-forming inverters to maintain stability.
These new models are crucial first steps for system planners to better understand how grid-forming inverters could impact their power grids.”
Grid-Following vs. Grid-Forming: A Paradigm Shift
Traditional electricity generation methods, like coal, gas, nuclear, and hydro, rely on spinning turbines that drive synchronous machines. These machines produce a stable AC voltage at a specific frequency. However, solar panels, wind turbines, and batteries produce DC, necessitating conversion to AC.
Current inverters on the grid are known as grid-following, meaning they control the current of electricity. They were designed when the grid had ample synchronous machines to maintain voltage stability. However, as the nation progresses towards a decarbonized grid, more fossil fuel plants will be retired.
Grid-Forming Inverters: A New Approach
To ensure grid stability, researchers are developing grid-forming inverters, which focus on controlling voltage rather than current. They also enable automated coordination with other inverters and synchronous machines on the grid, further enhancing system stability.
Modeling the Grid’s Future
Last fall, a WECC report explored how grid-forming inverters could maintain grid frequency stability during stress events, such as a sudden loss of generation. Using the new model, the report found that grid-forming inverters could significantly improve frequency response compared to conventional grid-following inverters as more renewable generation is integrated.
In a smaller-scale project, system operators at the Electric Reliability Council of Texas utilized the model to demonstrate how grid-forming technology can better support renewable connections in “weak” power grids, typically remote areas far from generation sources.
Real-World Demonstration in Oregon
While grid-forming inverters are not yet widespread, the promising results from the WECC report have spurred a renewable power plant in eastern Oregon to plan a demonstration of this technology by 2026.
This project, funded by the SETO Solar and Wind Grid Services and Reliability Demonstration Program, will be the first of its kind in the U.S. If successful, it will pave the way for wider adoption of grid-forming technology.
Continuing Research and Development
The development of grid-forming inverter models represents a significant advancement in ensuring grid stability and reliability as renewable energy sources become increasingly prevalent.
Continued research and collaboration are crucial to refine these models and facilitate a smooth transition to a more sustainable energy future.