A large interconnected power system consists of large and small generating stations and all stations must have same frequency. The objective of providing an Automatic Generation Control (AGC) is to maintain the system frequency at nominal value and the power interchange between different areas at their scheduled values. The main requirement of an interconnected AGC is to ensure that frequency of various bus voltages and currents are maintained at near specified nominal values, tie-line power flowing among the interconnected areas are maintained at specified levels, and total power requirement on the system as a whole is shared by individual generators economically in optimum fashion.