Abstract: Doubly-fed hydro turbine units have a higher response speed and a wider working head than those of conventional hydro turbine units. But application of doubly-fed generators and frequency converters requires more complicated control methods. First, this paper develops a new method based on the load optimization theory for finding the minimum unit flows on equal unit power curves to improve the optimization method of optimal speeds. Then, according to the theory of stator flux orientation vector control and through double-channel excitation and multivariable error superposition, we integrate the current hysteresis vector control into a doubly-fed turbine generator excitation control strategy and obtain a method for rapid generation of the trigger signals of voltage source converters. Finally, we construct a simulation model of the single-machine infinite-bus system with doubly-fed turbines and achieve a variable speed and constant frequency (VSCF) function. And the operation cases of changing the given power are examined and compared with the conventional cases. The results show that our new control method significantly shortens the adjusting time of power response of a hydropower station.

Key words: doubly-fed generator, excitation control, hydraulic turbine regulating, multivariable error signal