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Electricity is crucial to modern life. We rely on being able to plug devices in to the outlet in the wall, flipping a switch, and things working without a problem. But it is not that simple, the power grid, all of the infrastructure that delivers energy from the power plant to your home, is something of a balancing act.Ìý

In order for a grid to operate safely, supply must equal demand. The flow of electricity through the grid in the United States flows at a frequency of 60 Hz, if the supply increases more than the demand, the frequency will increase, while if the demand increases, or the supply dips, the frequency decreases. The vast array of hardware that makes up the grid and in electrical devices, such as transformers, motors, or electronics, have been designed to operate at a specific frequency. If the grid is unbalanced, and the frequency changes too much, equipment can be damaged, efficiency is reduced, and it can lead to overheating, system failures, and blackouts. Keeping the grid online, and safe, is a balancing act that requires sophisticated controls systems to make sure that supply always equals demand.

Think of the electric grid like a high-speed train system. In order for the train system to operate effectively all the trains need to maintain consistent speeds and keep to schedule, so passengers are not left waiting on the platform, or miss their trains because they left too early. Traditional power plants are like massive freight trains, that are super heavy and take a long time to speed up or slow down. These massive freight trains provide a kind of inertia to the whole system. They are hard to disrupt, which results in a consistent speed. Renewable energy sources, such as solar and wind, are more like fast, light commuter trains, that can change speed essentially instantly. They lack the inertia of the massive freight trains, but they can change fast. If it were up to just human conductors and train line controllers to regulate how the trains are running, having the freight trains and the commuter trains on the same lines would be near impossible, the difference in speed and inertia would make it really hard to reconcile. This is where advanced computer-driven control systems come into play. In the train analogy the smart predictive system would predictively control the brake and throttle of the commuter trains to ensure a simple constant speed. How would the grid be impacted if we developed a smart control system?

This new report details work led by RASEI Fellow Bri-Mathias Hodge, and discloses a new approach for smart control in the grid. The grid is already full of control systems, with the standard way power generators respond to frequency events being via linear droop control. This would be like a simplistic cruise control for one of the Commuter Trains in the above analogy. If the frequency drops a little, the system increases the power proportionately. The problem with this approach is that it often doesn’t use the inverters full capacity fast enough. The innovation described in this work is an update called Droop-e, a non-linear control based on an exponential function. Think of it like replacing the trains cruise control, which previously had a simple on/off switch, with a smart responsive gas pedal, that can speed up, or slow down, on a curve.

This change, from an on/off control to a responsive curve, has the potential to have significant impacts on the grid. By using the available power reserves more effectively, Droop-e reduces the number of severe power swings in the system, and results in a slower rate of change of frequency (ROCOF), which can buy grid operators valuable time to react to changes in frequency.

The benefits from the ‘shock-absorber’ properties that Droop-e offers could help prevent blackouts before they start, help stabilize the grid and improve integration of renewable energy sources, and create a smarter, more responsive grid, future-proofing systems by replacing the software, and not the hardware, a significant cost saving.

The simulations from this study confirm that this new control approach could improve the stability of grids that include a combination of traditional power plants and renewable energy generators. If a major power plant trips offline, this sophisticated control system activates un-tapped power reserves in batteries and renewables, acting as a hyper responsive shock absorber to protect the entire grid system. For grid operators, it means more time to react. For everyone with devices plugged into a power outlet, it means improved stability, and less equipment damage. It also provides a more effective mechanism to integrate different power sources, improving reliability, security, and affordability.