Persistent increase of power generation demand necessitates the use of modern
control techniques in power plants. These control techniques guarantees better
temperature and pressure control over wider range of operation in power plants, which in deed increases the power plant overall efficiency, by increasing the regular operating pressure and temperature of thermal cycle. For this means, generating a power plant simulator is an essential tool for analysis and controller synthesis. In this thesis, the details of the thermal cycle of Nekka power plant is analyzed in detail, and the structure and logic of the existing controllers are carefully determined. Then thermodynamical models for all subsystems of the power plant are developed, and their parameters are verified through input-output data extracted from the power plant. In regular operation these models are integrated into a computer simulation, in which the existing control system structure and logic is also implemented. The developed simulator can be used for the analysis of the existing controller structure, as well as, developing new strategies in controller design. A modern controller structure, using state feedback through state observer (SCO) is then proposed for the superheater of the power plants. Moreover, by using the developed simulator for the power plant, the effectiveness of the proposed controller in the behavior of the power plant is analyzed thoroughly. It is verified through simulations that using this structure for the control of the superheater, reduces the temperature error especially in load demand rapid changes, increases the life of superheater structure, reduces the maintenance costs, increases the rate of change of power demand, allows increasing the operating temperature and pressure of the power plant, and hence increases the overall power plant efficiency.