On Area Control Errors, Area Injection Errors, and Textbook Automatic Generation Control

We reexamine and critique the classical area control error concept used in automatic generation control, and propose a new error signal termed the area injection error. Unlike the ACE, the AIE uses direct measurement of generator power levels, yielding improved AGC performance in the presence of bias uncertainty and nonlinearity in generator turbine-governor responses. As a by-product of our analysis, we conclude that the effective frequency biasing found in a common textbook implementation of AGC is larger than intended, resulting in unintended interaction between control areas. Our theory is validated via simulations on a detailed two-area test system.