  Automatic generation control (AGC) is one of the most important coordinated
control systems present in modern interconnected power systems. Despite being
heavily studied, no interconnected dynamic stability and performance analysis
of AGC is available in the literature. This paper presents such an analysis for
a class of multi-area interconnected nonlinear power systems, providing a
nonlinear stability proof and examining dynamic performance from the
perspectives of non-interactive tuning, response speed, and sensitivity to
disturbances. The key insight is that dynamic stability and performance can be
rigorously captured by a reduced dynamic model, which depends only on the AGC
controller parameters and on the area frequency characteristic constants. Our
analytical results clarify some of the historical controversy concerning the
tuning of frequency bias constants in AGC for dynamic stability and
performance, and are validated by simulations on a detailed test system.
