EFFICIENCY BASED OPTIMAL-CONTROL OF KAPLAN HYDROGENERATORS

This paper investigates an optimal strategy for controlling the speed response of Kaplan hydrogenerating systems to decreases in load. Typic ally, primary control gates restrict and redirect water through the tu rbine to stabilize and transfer the system to operating point demand. The adjustable turbine blade angle is used to return to maximum operat ing efficiency at the new load level The over-speed reduction is limit ed by the conduit's ability to withstand the over-pressure caused by t he flow restriction at the turbine. A control scheme using gates and b lades simultaneously and independently is developed. The initial actio n of the proposed control moves the gates and blades in opposite direc tions at maximum rates in an effort to reduce efficiency without alter ing flow, thus quickly decreasing the generated power while affecting the pressure minimally. The final control action moves the gates and b lades simultaneously to restore maximum efficiency operation at the ne w power level demand. Similarities are found when comparing the effici ency based control to the Bang-bang and Linear Quadratic Regulator res ults of optimal control theory, though attempting to apply either of t hese methods directly to this problem is impractical. Simulation resul ts show that the proposed scheme outperforms the traditional gate-domi nant control in minimizing turbine over-speed and speed settling time under prescribed load change and conduit pressure limits. However, in its present form, the design is found to be more sensitive to system n onlinearities than its conventional counterpart.