Definition
Synthetic inertia, also called virtual inertia, is a control technique that makes an inverter-based resource — a battery, solar plant, or grid-forming converter — respond to frequency changes the way a heavy spinning generator would. Conventional generators resist frequency change because their rotating mass stores kinetic energy; as synchronous machines are displaced by inverter-based generation, that stabilizing inertia disappears. Synthetic inertia emulates it mathematically, injecting or absorbing power in proportion to the rate of frequency change.
How it works
A common approach embeds the synchronous machine's swing equation into the inverter's control software (a virtual synchronous generator). The inverter measures how fast frequency is moving — the rate of change of frequency — and counteracts it within milliseconds. The two practical goals are limiting RoCoF so protective relays don't trip, and arresting the frequency nadir so generation and load stay connected after a disturbance.
Relevance to inverter-heavy systems
For an off-grid or microgrid mining setup dominated by batteries and solar, synthetic inertia is what prevents small disturbances from cascading into instability. It is a proposed and increasingly deployed substitute for the physical inertia that conventional grids took for granted, and it works hand-in-hand with droop control and grid-forming inverters.
See also rate of change of frequency and the grid-forming inverter.
In Simple Terms
Synthetic inertia, also called virtual inertia, is a control technique that makes an inverter-based resource — a battery, solar plant, or grid-forming converter — respond…