Synthetic Inertia

Synthetic inertia is a control function that enables inverter-based resources to imitate part of the inertial response traditionally provided by synchronous machines. Instead of relying on naturally rotating mass directly coupled to grid frequency, the response is created by control algorithms that temporarily inject or absorb additional power when frequency changes rapidly.

This function has become more important as power systems replace synchronous generation with converter-based resources. Synthetic inertia does not reproduce every aspect of physical inertia, but it can help slow the initial frequency excursion and support system stability when designed and coordinated properly.

Key Aspects of Synthetic Inertia:

• Control-Based Response: Synthetic inertia is created by software and power-electronics control rather than by direct electromechanical coupling. The resource senses frequency or RoCoF and adjusts output according to its programmed response logic.
• Energy Source Requirement: Extra power must come from somewhere, such as battery energy, curtailed renewable headroom, or temporary kinetic-energy release from a wind turbine rotor. The quality of the response depends on how much energy and power margin is available.
• Frequency-Stability Benefit: The main purpose is to reduce the initial rate and depth of frequency decline after a disturbance. This can buy time for governors, reserves, and other slower frequency-control layers to act.
• Difference from Physical Inertia: Synthetic inertia is not identical to the passive, immediate response of a synchronous machine. It depends on measurement, filtering, controller settings, current limits, and recovery strategy, so poor tuning can reduce its value or create side effects.
• Grid-Code and Market Relevance: Many system operators are beginning to specify synthetic-inertia or fast-frequency-response capability for inverter-based plants. It is increasingly treated as a defined system service rather than an optional feature.