Power systems operation become more important as the load demand increases. Therapid increase in load demand forces power systems to operate near critical limits. The aimof power systems operation is to serve energy with acceptable voltage and frequency. In case of power system any small sudden load change in between generation and demand causes the system frequency to deviate from preset value. In Tana Beles HEP, synchronous generators have a default operating set point of ± 4% frequency deviation but practically at peak load hour the generators trip its circuit breaker. To minimize the problem, the operators, lower the generator frequency setting point to ±8% (46 Hz – 54 Hz).In a network, a drop in frequency could result in high magnetizing currents in induction motors and synchronous generators. This leads to the outage of generating units of Tana Beles HEP and will ultimately lead to total blackout of the whole system of the plant.The main purpose of the AGC is to balance the total system generation against system load and losses so that the desired frequency and power interchange systems are maintained. The role of an AVR is to hold the terminal voltagemagnitude of the generator at a specified levelwhich in turn, maintainsbus voltage.Power system stabilizers modeled to enhance the damping of power system oscillations in order to maintain the reliable operation of the grid. The conventional controllers are very slow in operation, ignores the nonlinearities of different power system component, unable to decide the gain of the integrator setting based on changes.So, FLC-PID has advantages over conventional PI or PID alone. They are much faster than integral controllers and also they give better stability response. So, this thesis work has been modeledand developed simulation of PSS and FLC-PID based AGC and AVR. The output power, speed and rotor angle deviation and generator terminal voltage is shown inMATLAB/Simulink.The simulation is carried out by AGC and AVR with (PID), (PID and PSS), (Fuzzy-PID) and(Fuzzy-PID and PSS). So, the Fuzzy-PID controller is highly improved the settling time while PSS controller is highly improved the damping oscillation. Thus, Fuzzy-PID based AGC and AVR with PSS is improved both damping amplitude oscillation overshoot,settling time and, steady state error of the system.