Definition
Automatic Generation Control (AGC) is the centralized, closed-loop system that continuously adjusts the output of participating generators to keep system frequency at its nominal value and to hold a balancing area's net power interchange with neighbors on schedule. It is the "secondary" layer of frequency control: where droop-based primary response acts autonomously within seconds, AGC issues coordinated commands every few seconds to restore frequency exactly to target and clean up the residual error.
Area Control Error
AGC works by computing the Area Control Error (ACE), a weighted combination of frequency deviation and tie-line interchange deviation. In North America, NERC reliability standards (such as CPS1 and BAAL) measure how well a balancing authority's AGC keeps ACE within bounds. The system raises or lowers dispatchable generation automatically to drive ACE toward zero.
Where flexible loads fit
Because AGC needs fast, controllable resources to follow its signal, fast-ramping assets are especially valuable. A curtailable mining load can in principle respond to AGC-style signals far faster than a thermal plant, making interruptible compute an emerging participant in grid balancing markets rather than only a passive consumer.
See also ramp rate and droop control.
In Simple Terms
Automatic Generation Control (AGC) is the centralized, closed-loop system that continuously adjusts the output of participating generators to keep system frequency at its nominal value…