Grid-forming inverter
An inverter that sets its own voltage and frequency reference, behaving like a voltage source that can stabilise weak grids and provide synthetic inertia.
Most solar, wind and battery inverters in service are grid-following: they use a phase-locked loop to track the existing grid voltage and inject current in step with it. They need a stable voltage waveform created by synchronous machines. A grid-forming (GFM) inverter instead behaves as a controlled voltage source behind an impedance, establishing voltage magnitude and phase angle itself, much like a synchronous generator.
Common control approaches include droop control, virtual synchronous machine (VSM) emulation and dispatchable virtual oscillator control. Capabilities include:
- Instantaneous response to phase jumps and frequency changes, providing synthetic inertia.
- Stable operation in weak grids with low short-circuit ratio (SCR below 3).
- Islanded operation of microgrids and potential black start.
- Damping of oscillations and voltage support during faults.
The constraint is current: power semiconductors can typically deliver only 1.1 to 1.5 times rated current during faults, versus 5 to 7 times for synchronous machines, so batteries with headroom are the most common platform. Notable deployments include the Hornsdale Power Reserve upgrade in South Australia (virtual machine mode, 2022), Kapolei in Hawaii and several Australian BESS projects. Great Britain's NESO introduced a GB Grid Forming specification and stability pathfinder procurements; AEMO, ERCOT and NERC are drafting GFM performance requirements.
Related terms
All terms →- Inertia (grid)
The kinetic energy stored in synchronously rotating generators and motors that resists sudden changes in grid frequency.
- Grid frequency
The rate at which alternating current changes direction on a power system, 50 Hz or 60 Hz, which reflects the instantaneous balance of supply and demand.
- BESS (Battery Energy Storage System)
A complete grid- or site-connected battery installation, including cells, battery management, power conversion, thermal management and controls.
- Microgrid
A local group of generators, storage and loads with defined boundaries that can operate connected to the main grid or independently in island mode.
- Black start
The process of restoring a power system after a total or partial blackout using units that can start without power from the grid.
- Variable renewable energy (VRE)
Renewable generation whose output varies with weather and time of day, mainly wind and solar PV, and cannot be fully dispatched.