Preliminary Study On Variable-Speed Constant-Frequency Technology In HydroPower Generation System

Conventional constant speed constant frequency hydropower generation system always takes up a dominant position in hydropower generation system. Due to the rotated speed of generator with constant speed constant frequency need a constant hydraulic turbine speed, the efficiency of unit is lower. Variable speed constant frequency(VSCF) hydropower generation system alters the phase. Hydrogenerator system with doubly fed generators (DFG) have superior performances such as good stability, ensuring variable speed constant frequency (VSCF), regulating active power and reactive power independently, and absorbing lag reactive power deeply. By the united control of DFG excitation system and the hydroturbine governing system, this hydrogenerator system can be operated round the optimal unit speed of hydroturbine, improved the hydraulic efficiency and optimized load regulation when the water level or water flux is changed.Hydrogenerator system with DFG is a synthetical system including water, hydroturbine and generator portion. In order to study the operation performances of this hydrogenerator system, it is very important to study the model of hydrogenerator system with DFG and its intelligent control strategies. The main contents in this thesis are as follow:1, The paper has introduced the mathematic model of the AC excited doubly-fed machine. Based on analysis of the internal electromagnetic relationship of DFG, the steady state operation performances of DFG are studied. And the paper has also introduced the mathematic model of cascaded brushless doubly-fed machine(CBDFM).2, Based on the load optimal regulation principle of hydroturbine, the load optimal regulation performances are analyzed at the same operation state for DFG and the conventional synchronous generator in terms of XIAO LANGDI hydroturbine regulation characteristics. The mathematical models of hydroturbine optimal regulation characteristics are established by using B spline function data fitting method.3, The mathematical models of the hydrogenerator system with DFG are establishedby using the small signal error method. Furthermore, a sufficient condition for the approximate stability in the large field of this generator system is preliminarily derived.