Automatic Generation Control (AGC) with secondary controllers is required to restore the frequency and tie-line powers to reference values. The scheduled tie-line power and uniform frequency can be obtained by using different secondary controllers like PID, PI-PD and ADRC controllers. Each state represents an area of power system controlled by the respective regulating authority, resulting in a multi area power system. Nowadays power systems are being deregulated. Hence studies of both regulated and deregulated hybrid power system are desired.Here AGC of multi area power systems is carried out in case studies to arrive at a good secondary controller. The simulation work is carried out using MATLAB Simulink software.