Automatic Generation Control

Design Features

PRISM AGC is an application that uses feedback loop control to regulate the power output of electric generators within a prescribed area in response to changes in system frequency, tie line loading, and the relation of these to each other. 


AGC monitors and controls power generation with these overall objectives:

  • Minimize area control error
  • Minimize operating costs, in conjunction with economic dispatch calculation software
  • Maintain generation at fixed (baseload) values 
  • Ramp generation in a linear fashion, according to a schedule specified by the operator 


PRISM AGC supports four states, which are dispatcher-selectable and/or automatically implemented by the AGC function listed below in increasing order of restrictions placed on them:

  • ON: All AGC functions are performed.
  • MONITOR: All AGC functions are performed except issuance of control action. 
  • ENTRY: Used for data entry when several quantities are to be entered, which would affect the output of the AGC function. 
  • SUSPEND: A state that is not selectable by the dispatcher but is implemented solely by AGC due to the sustained non-update condition of critical telemetered quantities.


AGC provides the following five operational control modes, each using a different method for calculating the area control error (ACE):

  • Tie-Line Bias (TLB) Control Mode
  • Constant Frequency (CF) Control Mode
  • Constant Net Interchange (CNI) Control Mode
  • Tie-Line Bias with Inadvertent Payback (TLB-IB) Control Mode
  • Tie-Line Bias with Time Error Correction (TLB-TEC) Control Mode


PRISM AGC allows the definition of up to four restricted (prohibited) operating regions for each unit. Each region is defined by upper and lower boundary values and permissible time value.


PRISM AGC supports the NERC CPS 1&2, DCS reporting and control requirements, as well as the ERCOT SCE (Scheduling Control Error) reporting and control requirements.

More Information

For more information call 800.831.7223 or contact This email address is being protected from spambots. You need JavaScript enabled to view it.