Abstract: Aimed at the research demand for variable speed hydropower unit control, this paper develops a numerical simulation model based on MATLAB/Simulink, focusing on the dynamic modeling and control strategy of the governor system of variable speed hydraulic turbines. We simulate the sudden loading and large load rejecting processes, considering the speed limitation and lag time of servomotor motion in the simulation of load rejecting, and examine their effects on the dynamic response of variable speed hydraulic turbines. Results show that (1) our newly-developed double PID control strategy, through considering speed errors and guide vane errors, can control isochronously the turbine speed and guide vane opening in steady state. (2) The load rejecting in operation of a variable hydraulic unit is similar to the case of a conventional fixed speed unit, resulting in excessive rise or fall of turbine speed and pressure. (3) During load adjusting, the speed limitation and lag time of servomotor motion have significant effects on the dynamic response of system variables, such as turbine speed, servomotor motion, pressure, and other unit parameters, thus limiting the amplitudes of primary frequency regulation and load regulation.

Key words: variable speed hydraulic turbine, variable speed governor, best efficiency track, pressure increase rate, speed increase rate