Hydroelectric Power Plants utilize the energy of flowing water to generate electrical power. Hence, these represent an important natural source of electric power in the world. Different types of hydraulic turbine used for power generation, like Pelton turbine, Kaplan turbine, Francis turbine etc. In a impulse (Pelton) turbine kinetic energy of the flowing water convert into rotating mechanical energy and for a reaction turbine (Francis, Kaplan) kinetic energy and the pressure energy both of the water convert into rotating mechanical energy. The power generated by the turbine depends upon the amount of water supplied to the turbine. To generate power at constant frequency demand power and generated power should be equal. The generated power will be change according to demand power. The water flow should be controlled by the inlet guide vane angle or by the spear opening of the nozzle to generate the power equal to demand power to maintain constant frequency. The controller design for the hydraulic turbine system become essential at this stage.