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Stabilizing grid frequency fluctuations through effective regulation
Traditionally, when energy demand exceeded generation, power plants would ramp up output, or backup generators would be used as emergency reserves. However, these methods take time to respond to sudden surges in demand. In contrast, renewable energy systems that use energy storage systems (ESS) can respond much faster. As more inverter-based generation is integrated, grid inertia decreases, leading to a higher rate of change in frequency. Quick and accurate responses to demand fluctuations are crucial for maintaining frequency stability. Frequency fluctuations are a good measure of grid performance, as balanced energy demand and supply lead to stable frequency.
With energy demand surges becoming more common, especially with more frequent weather events such as heat waves and cold snaps, addressing this problem at the design phase prepares energy suppliers for contingencies. If demand exceeds a system’s generation capacity, protective devices may trip, resulting in reliability failures.
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The Load Shed Service for imports (LSSi) is one solution to address rapid frequency fluctuations. This approach, currently used by AESO, counters frequency fluctuations at rapid rates where loads are taken offline quickly to mitigate the effect of sudden losses in energy imports. (1) Essentially, this strategy allows any system to mitigate the adverse effects of frequency drops when energy demand exceeds current generation capacity.
While loads are offline, the system’s generation capability can be ramped up. When the required supply is restored, the loads can be brought back online. Configuring a generation site in this manner minimizes the rate of change in frequency, thereby reducing the risk of reliability failures. Maintaining minimal frequency fluctuations is highly desirable in grids with a high proportion of inverter-based generation resources.
Over the years, various approaches have been explored for implementing frequency regulation in both new and existing systems, each with different operational speeds.
The most common method for achieving rapid responses to energy demand surges is through the use of energy storage systems (ESS). These systems can absorb or supply power from and to the grid within seconds. ESSs come in various forms, including battery-energy storage systems, mechanical storage and thermal storage. (2)
Another example involves wind power plants, where the pitch angle and speed of turbines can be adjusted in response to frequency changes. This adjustment allows the turbines to operate at maximum power point, supplying additional energy back into the grid. (2)
Moreover, electric vehicles (EVs) can provide a relatively fast frequency response while they are being charged. EVs have high energy response rates because on-demand power is essential for their operation and safety. This approach is currently being explored as a viable solution for the future, especially as EVs become more prevalent. (2)
Having the ability to quickly counteract frequency fluctuations is becoming a key component in designing new energy generation systems. As the global shift toward renewable sources continues, grid inertia is decreasing due to increased use of inverter-based generation technologies. Lithium ion-based battery energy storage systems are becoming more popular, offering a relatively low cost per kWh and enhancing grid reliability.
Sources:
- Alberta Electric System Operator, « Load Shed Service for imports », Market Participation, 2024, https://www.aeso.ca/market/market-participation/ancillary-services/load-shed-service-for-imports/
- Hassan Alsharif, Mahdi Jalili, Kazi N. Hasan, Fast frequency response services in low inertia power systems—A review, Energy Reports, Volume 9, Supplement 10, 2023, Pages 228-237, ISSN 2352-4847, https://doi.org/10.1016/j.egyr....(https://www.sciencedirect.com/...)
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