Diversity can prevent major power grid failures

The electric power grid works with the main areas for improvement and research. Photo: Matthew Henry

Recent power outages in Texas have drawn attention to its electricity grid is separated from the rest of the country. While it is not immediately clear whether full integration with other parts of the national grid would eliminate the need for power outages, the state's inability to import significant amounts of electricity was a crucial factor in the resulting power outage.

A large power grid has perks but also has dangers that researchers at Northwestern University hope to address in order to speed up system integration and improvements.

The obvious problem with large grids is that failures can spread further - in the case of Texas, across state lines. The other is that all power generators must be synchronized to a common frequency in order to transmit power. The US is served by three "separate" networks: The Eastern Link, the Western link, and the Texas Link interconnected only by direct current power lines. Any constant frequency deviation in the region can lead to downtime.

As a result, researchers are looking for ways to stabilize the grid, looking for methods to mitigate deviations in the frequencies of electric generators.

A new Northwestern study shows that contrary to the assumptions made by some, there is a stability advantage of heterogeneity in the power grid. Studying several power grids in the US and Europe, a team led by Northwestern physicist Adilson Motter recently reported that generators operating at different frequencies return to normal faster when they are wetted by "switches" at different speeds than the generators around them.

The paper was published on March 5 in the journal Nature Communications.

Motter is a professor of physics and astronomy at the Weinberg College of Arts and Sciences. His research focuses on nonlinear phenomena in complex systems and networks.

Motter compares the electric grid to a choir: "It's a bit like a choir without a conductor. The generators must listen to the others and speak synchronously. They react and react to each other's frequencies."

Listen outside of the beat frequency, and there may be a crash as a result. Given the interconnected components of the system, a failure can spread across the entire network. Historically, these failures were prevented by using active controllers. However, failures are often caused by management and hardware errors. This indicates the need to create additional stability within the design of the system. To achieve this, the team looked at using natural grid inhomogeneities.

When the oscillator frequencies move away from the synchronous state, they can swing for a long time and even become more unstable. To mitigate these fluctuations, they came up with something similar to a door mechanism used to close the door faster, but without slamming.

"Mathematically, the problem of damping frequency deviations in a generator is analogous to the problem of optimally damping a door to make it close the fastest, which has a known solution in the case of a single door," Motter said. "But this is not one door in this analogy. It's a network of many doors that are connected to each other if you can imagine the doors as power generators."

By creating an "optimal damping" effect, they found that instead of making each damper identical, damping the power generators in a way that is appropriately different from each other can further optimize their ability to synchronize at the same frequency as quickly as possible. That is, sufficiently non-uniform damping across the entire network can lead to increased stability in the power grids studied by the team.

This discovery could have implications for future grid design, as developers work to optimize technologies and in considerations of further integration of now-separated networks.

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