Traditional grids are stabilised by huge spinning synchronous generators whose rotating mass provides inertia — a buffer that resists sudden frequency changes. As coal and gas plants retire and inverter-based solar and wind take over, this inertia disappears, threatening stability. Grid-forming inverters are the answer: they actively create voltage and frequency rather than passively following.
Working principle
Today's standard grid-following inverters use a phase-locked loop to synchronise to an existing grid voltage — they cannot operate without it. A grid-forming inverter instead behaves as a controllable voltage source with its own internal reference, often emulating a generator via virtual synchronous machine or droop control. It can set frequency, ride through disturbances, supply synthetic inertia and even black-start a dead grid.
| Capability | Grid-following | Grid-forming |
|---|---|---|
| Reference | External (PLL) | Internal |
| Inertia | None | Synthetic / virtual |
| Islanded operation | No | Yes |
| Stability role | Passive | Active stabiliser |
Why it mattersStability in a low-inertia grid is the defining challenge of the energy transition; grid-forming control is now mandated in several jurisdictions for large new storage and renewable plants.
Applications
- Battery storage providing inertia and black-start
- Remote / island microgrids running on solar + storage
- High-renewable transmission systems maintaining stability
References & further reading
- Rocabert et al., “Control of Power Converters in AC Microgrids,” IEEE Trans. Power Electronics, 2012.
- Lasseter et al., “Grid-Forming Inverters: A Critical Asset for the Power Grid,” IEEE JESTPE, 2020.
- NERC, “Grid Forming Technology — Reliability Guideline,” 2021.