Pelton turbine deflector overspeed control for a small power system

The overspeed deflector control of two Pelton turbine hydro units in the Alaska Railbelt power system has caused many incidents of oscillatory instability. Among the causes is the high controller gains applied to the deflectors, which are essential for load rejection operations but destabilize the power swings. In this paper, the overspeed control is achieved by reducing the feedback gains derived from frequency-domain analysis and using an adaptive feedforward control to counter the transient overfrequency condition. Simulation studies show the improved performance of the proposed control design.