Research On Brushless Doubly-Fed Power System Applicated In Small Hydroelectric Station

Small hydropower stations are often built on small rivers and dams,etc.,with a run off unstable,Head volatile characteristics,require a wider range of speed operation.The brushless doubly-fed generator(BDFG)adopts a variable-speed constant-frequency(VSCF)power generation method,which can adjust the rotation speed by adapting to the change of the water head to improve the efficiency of the hydropower generating unit.Meanwhile,the requirement of small sized converter and the absence of brush can not only decrease the cost of manufacture and maintenance,but also improve the stability of the generator system.First,the application background of brushless doubly-fed small sized hydroelectric generation technique and its development status are introduced and a preliminary introduction to variable-speed constant-frequency power generation is gave.Then,the fundamental principle of brushless doubly-fed hydroelectric generator is analyzed.Concretely,the operating characteristic and basic theory of hydro turbine and brushless doubly-fed machine are studied;the generating efficiency and maximum output can be improved by regulating the operational speed under different hydraulic head and load;the method of operational speed regulation during the optimization process is also studied.The control strategy of grid connected BDFG is researched in the third part.Based on the voltage stability characteristics of grid-connecting,the model of the machine is simplified by applying grid voltage vector orientation control.The comparison of phase-locked loop(PLL)during the voltage orientation process under different grid environment is analyzed,which provides coordinate system reference for the grid-connecting algorithm and operational control.As for the grid-connecting algorithm of BDFG,grid-connecting switching control strategy and power decoupling control strategy are mainly studied.The combination of indirect vector control and closed-loop compensation is applied to simplify the control algorithm and enhance the robustness which can resist the parameter disturbance of the control system.Lastly,the control algorithm of grid-side voltage stabilized converter is researched.What's more,the simulation model is built in Matlab/Simulink,which is used to verify the validity of the control system.Finally,the characteristics and controlling performance of the generator system are tested by the brushless doubly-fed grid connected generator system experimental platform.Based on the results of the experiment and the operation of Beishan hydroelectric station which applies the generator system,the application advantages of the system in the region of small hydroelectric station can be completely verified.