Synching Up a Reliable Power Grid

Monday, March 4, 2013 @ 04:03 PM gHale

As the national power-grid network becomes larger and more complex, achieving reliability across the network is becoming increasingly difficult.

Conditions and properties are available for utilities to use to keep power generators in a synchronized state and help make a self-healing power grid a reality.

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This new type of design for a better power grid could help reduce the frequency of blackouts and the cost of electricity as well as offer an improved plan for handling the intermittent power sources of renewable energy, such as solar and wind power, which can destabilize the network, said researchers at Northwestern University.

“We will be looking at a completely different power grid in the future,” said Adilson E. Motter, the Harold H. and Virginia Anderson Professor of Physics and Astronomy at Northwestern’s Weinberg College of Arts and Sciences, and leader of the research project. “The use of renewable energy is growing. More people will be driving electric cars, and the power grid will be delivering this energy, not gas stations. We need a power grid that is more capable and more reliable. This requires a better understanding of the current power grid as well as new ways to stabilize it.”

The crux of the challenge is for the U.S. power grid to function the power generators in each of its three interconnections (Eastern, Western and Texas) must be in synch, all operating at the frequency of 60 hertz. Out-of-synch power generators can lead to blackouts that affect millions of people and cost billions of dollars — losses similar to those of the Northeast blackout of 2003.

Having a network that can synchronize spontaneously and recover from failures in real time — in other words, a self-healing power grid — could prevent such blackouts. To help achieve this, power companies could apply the Northwestern guidelines as they add power generators to the network or tweak existing generators.

The research team wrote a paper describing the mathematical model, entitled “Spontaneous synchrony in power-grid networks.”

When a problem develops in the power-grid network, control devices return power generators to a synchronized state. Motter likens this to using medicine to treat someone who is ill. He and his colleagues are suggesting conditions to keep synchronicity in good shape so interventions stay at a minimum.

“Our approach is preventive care — preventing failures instead of mitigating them,” said Motter, an author of the paper and an executive committee member of the Northwestern Institute on Complex Systems (NICO). “The guidelines we offer could be very useful as the power grid expands.”

Researchers derived a condition under which the desired synchronous state of a power grid is stable. They then used this condition to identify tunable parameters of the power generators that result in spontaneous synchronization. This synchronization can be autonomous, not guided by control devices.

“The blackout at this year’s Super Bowl was caused by a device that was installed specifically to prevent blackouts,” said Takashi Nishikawa, an author of the paper and a research associate professor of physics and astronomy at Northwestern. “A large fraction of blackouts have human and equipment errors among the causes.

“Reduced dependence on conventional control devices can improve the reliability of the grid,” he said. “Our analysis also suggests ways to design control strategies that potentially can improve the existing ones.”

Power generators are very different from each other; some are large and others small. Motter and his colleagues identified a “body mass index” for power generators, which they suggest should be kept approximately the same (making, in essence, all generators look the same to the network) in order to strengthen spontaneous synchronicity in the system. If the body mass indices change, they should change in a coordinated way.

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