Grid-Forming Inverters: Why Power Systems with More Renewables Need Them

A grid built around spinning machines

For a century, power systems were dominated by synchronous generators. Their rotating mass provides inertia that slows down frequency changes after a disturbance, and they act as voltage sources that keep the grid “stiff”. Protection systems and operating practices grew up around this behaviour.

The rise of inverter-based resources

Solar PV, wind turbines and batteries connect through power electronics. Most of them today use grid-following control: a phase-locked loop measures the grid voltage and the inverter injects current in step with it. This works well when the grid is strong. When many synchronous machines go offline, the grid becomes weaker, and grid-following inverters can struggle or even interact in unstable ways.

What grid-forming means

A grid-forming inverter behaves more like a voltage source. It sets its own voltage magnitude and frequency and adjusts them in response to power flows, often using control schemes such as droop control or virtual synchronous machine emulation. As a result it can:

• contribute fast, inertia-like response to frequency events;
• support voltage and system strength in weak areas;
• help restart parts of a network (black start) when designed for it;
• operate in islanded microgrids.

Challenges

Inverters have limited overcurrent capability compared with rotating machines, so fault behaviour must be designed carefully. Grid codes and testing methods are still evolving, and system operators need models that represent grid-forming behaviour accurately in studies.

Why it matters for engineers

Grid-forming batteries are already being deployed to support networks with high shares of renewables. Engineers who understand power electronics, control and power-system stability are in demand. Explore our energy and networks programmes, and see how battery packs are kept within safe limits in our article on battery thermal management.