In this thesis, at first, a precise and nonlinear model is developed for Nekka power plant turbine from its real data and documents. We proposed to use boiler-turbine coordinated control system to increase effective efficiency of the steam unit. Identification procedures have been performed to obtain continuous time models of Nekka steam turbine at various loads. After determining the upper bound for uncertainty and choosing a good performance weighting function, a robust controller was designed and implemented in closed loop for the turbine nonlinear model. However, the closed loop performance was not suitable. In the next stage, a cascade controller structure in which the turbine loop was closed by a PI controller is proposed in order to significantly reduce the uncertainty. By using this structure, a new controller was designed for the system. Simulation results demonstrate very suitable performance of closed loop system with this new controller in terms of tracking, speed of response, and damping of oscillations.