Smoothing out frequency fluctuations on low-inertia islands and electrically islanded grids

Islands and electrically islanded grids have traditionally relied on diesel and other fossil fuels to cover their power generation needs. As both the economic and environmental costs of importing fossil fuels continue to rise, increasing the amount of renewable generation to offset diesel generation costs is becoming a more attractive option. However, the fragility of many island systems can make operators leery of introducing too many distributed energy resources—especially ones like solar PV and wind—which offer intermittent power and can exacerbate frequency management issues. 

Island power networks tend to have low system inertia, which can make them less resilient to power frequency fluctuations, wreaking havoc on equipment and potentially destabilizing the grid. Under frequency load shedding (UFLS) events are a regular threat on low-inertia grids much more so than on larger grids, making frequency management a critical issue on island grids.  

A traditional approach to shoring up frequency and grid stability is to back the grid with diesel generators, which defeats the purpose of adding more renewables to support decarbonization efforts. Plus, the latency associated with diesel generator start-up can be too slow for the microsecond correction that needs to happen to avoid significant frequency fluctuations, leading to a chain reaction related to load imbalance as equipment shuts down and takes itself offline to protect itself from the frequency anomaly.  

A new approach, one that takes advantage of fast-responding inverter-based resources like batteries and solar PV, is readily available on the market today. Some folks believe that equipping the island grid with grid-forming inverters will solve the problem. Unfortunately, experience has shown that it’s more complicated than that. If the grid-forming inverters aren’t coordinated, their actions will become unsynchronized as they compete with one another to ‘correct’ the grid disturbance.  

The solution lies in a layer of control that has oversight and management of all the resources, is network aware, and can respond within milliseconds, or one cycle, to dispatch resources accurately so each plays its role in restabilizing the grid as part of an orchestrated system, rather than each in isolation. Essential to this system is a battery energy storage system (BESS), which the controller can leverage to instantly inject or absorb power as needed. Such a BESS can have a primary role of frequency regulation during steady-state operation and can provide synthetic inertia in the form of a rapid dispatch of energy during shortfalls such as those caused by cloud cover suddenly arriving over a solar PV farm. 

Islands and electrically islanded systems have a unique and exciting role to play as the world’s transmission and distribution networks wrestle with the challenges of the 21st century grid. They are the ideal proving grounds for demonstrating how grids with a high percentage of renewables can be stabilized with new technology. Given that low-inertia grids tend to be more vulnerable and have fewer redundancies than larger, well-connected grids, if stability can be achieved on an island, those same results can be scaled up for larger grids as they become saturated with renewables and distributed energy resources.  

If you’d like to learn more about this topic, download our Island frequency management guide and share it with associates wrestling with island frequency management issues in the face of rising renewable energy resources.