What is synthetic inertia?

• A. Inertia slows frequency changes; conventional generators provide inertia, while inverter-based renewables reduce physical inertia and may require synthetic inertia or grid services.
• B. Inertia is no longer relevant in modern grids.
• C. Inverter-based renewables automatically increase system inertia.
• D. Synthetic inertia is never used in modern grids.

Answer: (A)

Inertia is the grid’s resistance to rapid changes in frequency, provided mainly by the spinning masses of conventional generators. When a disturbance happens—like a generator trips—the kinetic energy of those rotating machines helps to slow down the initial frequency decline, giving time for automatic governors and other actions to respond. As more inverter-based renewables come online, there’s less rotating mass in the system, so the natural inertial response decreases. To keep frequency stable, these resources can provide synthetic inertia: fast, electronically controlled adjustments that mimic the inertial effect by injecting or curbing active power in response to frequency changes. This often involves specific inverter controls or grid services. So the best answer recognizes that inertia slows frequency changes, conventional generators provide inertia, inverter-based renewables reduce physical inertia, and synthetic inertia or grid services may be needed to compensate. Inertia is still relevant, and synthetic inertia is indeed used in modern grids; inverter-based resources don’t automatically increase inertia without such controls.