Research On Theory Of Modeling And Control Of Double-Fed Pumped Storage Units

With the substantial development of China’s economy and the expending scale of the grid, the demand for power quality has become increasingly significant instead of the simple requirement of the limitation on the amount of the demand load. Consequently, the pumped storage power station has become more and more important in the power system. In order to make the pumped storage power station play fully the role of adjusting the peaks as well as the frequency, the DFIG (doubly fed induction generator) motor is used instead of the synchronous motor. The operating statue of the generation units can be regulated quickly by adjusting the rotor voltage amplitude, phase and frequency through the inverter with the result of the adjusted operating state of the unit, improved efficiency and enhanced system stability. In this thesis, the control strategy of the DFIG inverter is researched deeply based on analysis of the basic theory of the DFIG, and the corresponding control countermeasures is put forward based on the control design demand of pumped storage units, and complete the modeling and simulation in Matlab/Simulink simulation software. Lastly, the simulation results can verify the feasibility of the control strategy. The main work of this study is followed:(1) The power flow regular of the DFIG under different operating modes is analyzed with analysis method of vector diagram. Then the different mathematical models of the DFIG are established separately under a-b-c stationary coordinate system and synchronous rotating coordinate system.(2) According to the structure of the AC-DC-AC inverter and the vector control principle, the active and reactive power control of both the rotor-side and the grid-side inverter is proposed. The decoupled equation of speed and reactive power control is also described and the observation method of the stator flux is proposed. Set up a control strategy model. The simulation model of the4kw DFIG is set up by Matlab/Simulink simulation software. And the situation of power changes, adjusting speed and stator voltage fluctuation is simulated. The results of the simulation verify these two kinds of control methods can realize decoupling control, the control precision is within2%, and it can response within0.01s. Compared with the traditional synchronous motor in the power grid voltage fluctuations, it can improve the stability of the motor.(3) During the simulation, control of power priority under the modes of power generating condition is used according to the requirements of the double fed pumped storage unites under the modes of power generating condition and the electric condition. Based on the ideals of pump-turbine model, the model of doubly-fed pumped storage unit of250MW is established in Matlab/Simulnik. Through simulation analysis of the change in power, in power generating condition the expense of rotor can adjust the unit active power of125MW at the ls and the input active power can be adjusted to125MW within0.7s due to the electric condition. Meanwhile, the track of optimal efficiency speed can be achieved and the highest efficiency of the pump-turbine can be maintained in both power generating condition and electric condition. The theoretical approach of decoupling control for the doubly-fed pumped storage unit is provided.