What Is Grid Forming?

Grid forming, abbreviated GFM and also written grid-forming, is the inverter control strategy in which a power converter regulates the magnitude and phase of its own output voltage and allows current to be set by the network it is connected to. A grid-forming converter behaves as a controllable voltage source behind an impedance, which is the same external behavior a synchronous generator presents. Because it establishes a voltage waveform rather than tracking one, it can energize a network on its own, operate an island, and share load with other sources without needing an external phase reference.

The concept originated in uninterruptible power supplies and standalone microgrids, where no external grid exists to follow. It moved into bulk power system engineering as inverter-based resources displaced synchronous machines and system operators began to face networks with too few voltage-forming devices. The National Renewable Energy Laboratory's research roadmap on grid-forming inverters frames these controls as central to operating a future North American power system in which inverter-based resources supply the bulk of generation.

Control Architectures

Several control families produce grid-forming behavior. Droop control sets output frequency as a decreasing function of active power and voltage magnitude as a function of reactive power, reproducing the load-sharing characteristic of a governor and an automatic voltage regulator. Virtual synchronous machine and synchronverter schemes go further by numerically integrating a swing equation inside the controller, so the converter presents programmable inertia and damping. Matching control instead maps the converter's DC link voltage onto machine states, an approach developed in work on grid-forming control based on matching synchronous machines. Dispatchable virtual oscillator control synchronizes converters through a nonlinear oscillator law and offers provable stability guarantees for parallel units.

Current Limiting and Fault Behavior

The central difficulty is that semiconductor switches tolerate only modest overcurrent, typically 1.1 to 1.5 times rated current, while a voltage source facing a nearby fault would naturally push far more. Grid-forming designs therefore need a limiting scheme that constrains current without destroying synchronism, since a converter that saturates its current loop temporarily stops behaving as a voltage source and can lose angle stability when the fault clears. Virtual impedance, current reference saturation with anti-windup, and mode switching between voltage and current control are the common approaches, and a guide to current limiting and stability with grid-forming inverters catalogs the tradeoffs among them. Protection coordination is affected as well, because relays calibrated for the several-fold fault current of a synchronous generator see a much smaller signature.

System Services and Black Start

Grid-forming converters supply services that were previously byproducts of rotating mass: instantaneous response to rate-of-change-of-frequency events, voltage regulation at the point of connection, damping of inter-area oscillations, and a stable reference for surrounding grid-following devices. Battery storage plants in South Australia, Great Britain, and the Electric Reliability Council of Texas footprint have been commissioned with grid-forming firmware and used in black start trials, where a converter energizes a dead network section before conventional units resynchronize. Coverage in IEEE Spectrum describes how these capabilities are being written into interconnection requirements rather than left as optional features.

Applications

Grid forming has applications across a range of power engineering contexts, including:

• Battery energy storage plants providing inertia and frequency response
• Islanded and campus microgrids, including military and remote sites
• Black start and system restoration after a wide-area outage
• Offshore wind farms connected through high-voltage direct current links
• Photovoltaic plants in weak or low-short-circuit-ratio networks
• Uninterruptible power supplies and shipboard power systems