Yilu Liu is an expert in smart-grid technology, and has developed several different inventions used to monitor the electrical grid on a large scale. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy
Yilu Liu, an electrical engineer and the current UT-ORNL Governor’s Chair at the University of Tennessee and Oak Ridge National Laboratory, has once again been recognized by the R&D 100 Awards, an annual competition known as the “Oscars of Invention.”
A technology Liu and her colleagues developed, the InertiaMeter, was chosen as a winner by R&D World, the magazine that puts on the event, and also garnered a silver award in a special recognition category, “Green Tech.”
The InertiaMeter offers a new means of monitoring fluctuations in the flow of electricity in the grid, which is subject to the push of power generation and the pull of demand and needs to be kept in balance for the overall functioning of the nation’s electrical system.
“Knowledge of system inertia will allow grid operators to make decisions on when to request artificial inertia and how much is needed,” Liu said about the InertiaMeter’s broader impact. “The technology will help ensure our nation’s electric power grids could operate with 100% carbon free and renewable sources.”
As the name of Liu’s invention suggests, a key component of a reliable electrical grid is a certain amount of inertia, which broadly speaking is the tendency of objects in motion to stay in motion unless a countering force like friction stops it. In this case, the objects in motion are the rotating systems like steam turbines, which are directly connected to the grid. Electrical systems centered on traditional power sources – large turbines powered by water, fossil fuels, gas or nuclear energy — have a good deal of inertia built in. These turbines continue to spin for a time after their operations are disrupted, giving grid operators a narrow but crucial window to rebalance the system and keep the grid stable: The average conventional power plant has an inertia constant ranging from two to seven seconds.
In the past, grid operators could take inertia in the system for granted, and did not actively monitor it. When it was necessary, grid inertia was calculated by adding up all inertia values of big generators that are dispatched. However, grid operations are changing due to the increasing prominence of variable and intermittent sources of energy, such as renewables like wind and solar, which have little or no inertia. To successfully integrate them into the grid, operators need to have a real-time measure of the overall inertia in the system.
That is where the InertiaMeter comes in. The InertiaMeter is based on a new algorithm that calculates inertia using a signal that’s produced by a particular form of hydropower energy, pumped storage plants. A pumped storage plant generally consists of two connected water reservoirs at different elevations. Water is pumped to the higher reservoir during times of low electrical demand, then released to the lower reservoir when demand is high. The falling water spins a turbine on the way down, generating electricity. The immediate electrical capacity of pumped storage plants is primarily used to keep electricity flowing evenly, and can forestall blackouts in the event of a generator shut down elsewhere in the grid. Liu and her colleagues discovered that they could use pump shut-off data, which is much more frequent and regular than spontaneous disruptions to the grid, to estimate the overall inertia in the system.
The result is a new method that is highly accurate, requires no additional equipment and is easy to implement, Liu and her co-authors said in a recent conference paper. The judges at the R&D 100 Awards took note of the elegant solution provided by the InertiaMeter.
Liu said it was a group effort, and expressed appreciation for those who were involved.
“This project was successful thanks to the efforts of ORNL’s Water Power Program staff, specifically Shih-Chieh Kao, Hope Corsair and Lora Davis,” Liu said. “Shih-Chieh’s team was wonderful to work with. Industry support from the Tennessee Valley Authority, the Pacific Gas and Electric Company and Dominion Energy was also indispensable.”
Liu is no stranger to the R&D 100. She has won three R&D 100 awards in the recent past for other grid-related technologies she has developed, taking home honors in 2018, 2021 and 2022.
She is in good company. Researchers at ORNL will be well-represented at the award ceremony on November 21, 2024, in Palm Desert (near Palm Springs), California. The laboratory will receive 14 R&D 100 Awards in all.
This project was supported by U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy and Water Power Technologies Office (WPTO), through a program called the HydroWIRES (Water Innovation for a Resilient Electricity System) Initiative.
UT-Battelle manages ORNL for the DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science. — Clare Kennedy
