Automatic generation control

Automatic generation control adjusts generators’ real-power output to keep grid frequency near its nominal value and maintain scheduled power exchanges between interconnected areas.

Area control error: A control signal combining an area's frequency deviation with deviations in its scheduled interchange. AGC uses this signal to decide whether an area should raise or lower generation.
Grid frequency: The rate of oscillation of alternating current in an electric power system. Frequency deviations reveal instantaneous imbalance between generation and demand.
Automatic frequency restoration reserve: A balancing reserve activated automatically to restore frequency and control-area interchange after disturbances. AGC commonly activates this reserve through generator setpoint adjustments.
Frequency regulation: The balancing of generation and demand to keep power-system frequency within an acceptable range. AGC performs sustained regulation after fast local responses have arrested a disturbance.
Load-frequency control: The control of generation to limit frequency deviations and restore nominal frequency after power imbalances. AGC is the supervisory implementation of this broader frequency-regulation function.
Active power: The average rate at which electrical energy is transferred or converted into useful work. AGC changes generators’ active-power output rather than their reactive-power output.
Economic dispatch: The allocation of generation among units to meet demand at minimum operating cost, subject to constraints. AGC can distribute regulation commands among units while respecting dispatch schedules.
Inter-area oscillation: A low-frequency oscillation in which groups of generators in different regions swing against one another. Poorly tuned or coordinated control can interact with these oscillations.
Frequency bias: A coefficient that relates frequency deviation to the power response expected from a control area. It determines how frequency error contributes to area control error.
Interconnected power system: A network of power systems linked by transmission lines and operated with coordinated exchanges. AGC maintains schedules between the control areas that make up such a system.

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