Grid Forming Inverters

Reports on the Iberian blackout of April 2025 point out concerns with voltage management and the capability of facilities to automatically support the grid during disturbances. One of the key technologies being integrated into grids around the world is the grid forming (GFM) inverter. All the inverters (and wind generator controls) in the Texas Interconnection today are known as grid following (GFL) because their electrical current output depends on tracking the grid waveform provided by synchronous generation, using a control feedback technique known as phase-locked loops.

Basically, a GFL inverter injects or absorbs active or reactive power by controlling its output current while using the grid waveform as its guide. In contrast, a GFM inverter works as a voltage source that sets the amplitude and frequency of the grid, more like a synchronous rotating generator does. There are trade-offs with either approach and the industry found it advantageous to build GFL inverters initially, especially when the penetration of renewables and battery energy storage systems (BESSs) was a low proportion of total grid capacity. However, as the percentage of grid capacity from inverters grows, the benefits of GFM are becoming clear—especially when paired with BESS that have stored energy (solar and wind essentially operate as if they are continually at maximum capacity; BESS can draw on its charge to increase output).

Support of frequency with more inertia-like characteristics is one benefit, but the ability of GFM inverters to increase short-circuit strength in electrically weak areas of the grid (like West Texas) is particularly desirable. GFM can also support oscillation dampening in the grid. Interest in this technology is high given the immense growth forecasted of BESS in our Region and the successful demonstrations of GFM in Australia, Ireland, and other countries.

The Electric Reliability Council of Texas (ERCOT) proposed requiring GFM capability in NOGRR272 for new BESS with signed interconnection agreements after January 1, 2026. Resource owners have also proposed creation of an “advanced grid support” ancillary service in NPRR1278. The addition of GFM-equipped BESS, with careful study and setup, could provide support along with new synchronous generation, synchronous condensers, and dynamic reactive compensation devices to strengthen the weak areas of the grid and improve stability. This is critical given the rapid growth in both GFL-based facilities and large electronic loads like data centers that are highly sensitive to voltage fluctuations. GFM may offer other capabilities that GFL does not—such as the ability to provide initial blackstart service.