| Wind power generation has been developing quickly in resent years. The VSCF (Variable Speed Constant Frequency) wind power generation is a new technology. The study on the control technique of the VSCF wind power system is of great significance for improving wind power generation technique, and developing wind power systems that possess the self-intellectual property of our country. Based on the relative technique research and the demand of developing VSCF wind power generation technology in our country, this thesis presents a deep study on the excitation control technique of the VSCF doubly fed wind power generator. The main contents of the thesis are as follows.Using the stator field orientation vector control theory in the d-q axis synchronous rotating reference frame, the expressions of output power and excitation control parameters of doubly fed generator have been established, which effectively reflect the function of the amplitude, phase angle and frequency of the rotor excitation current for controlling the output power. The power control model and simulation results show that the asynchronous component of the active power and the uncontrollable component of the reactive power possess the feature of the induction machine; and the synchronous component of the active power and the controllable component of the reactive power possess the feature of the synchronous machine. This analysis method shows the operation feature and control characteristic of the doubly fed generator, which provides the basis for the studying excitation control technique of the VSCF doubly fed wind power generation systems.Power factor can not only be observed easily but also reflect the relationship between the active power and reactive power as well as the excitation situation. For the first time, this thesis puts forward the excitation control strategy of the doubly fed generator using the power factor as the main observing parameter, deduces the relationship between the power factor, rotor voltage and generator parameters, analyzes the influence of parameter variation on the power factor and output power, and presents a new method for studying the excitation control technique of the VSCF doubly fed wind power generator.A mathematic model of converter in the d-q axis synchronous rotating reference frame is proposed for the first time. The model shows clearly the hardware structure and control parameters of the rotor excitation system, as well as the relationship between the control system and generator model, which is helpful for the analysis of wind power generation system. A windpower generation system model including variable pitch wind turbine, doubly fed generator and VSCF control system is established, the system simulations are carried out, and the optimal power control strategy of the doubly fed generator is studied for different operating modes.The waveform optimization technique of the PWM inverter for the rotor excitation control system is also studied. A control algorithm of SPWM (sine pulse width modulation) based on 8XC196MC single-chip-computer is proposed. Through the improvement of carrier wave ratio selection and algorithm, the symmetry of the three-phase output voltage waveform of the inverter can be guaranteed, and the harmonic components can be reduced. The experimental results of the prototype machine show that the proposed SPWM control technique is practical.An experimental system of VSCF doubly fed power generation system based on 8XC196MC as the central control unit has been built and the experimental study of the excitation control technique has been carried out. The VSCF control and the soft-connection of the generator to the grid are realized. Two control strategies of the rotor excitation mode, "AC-DC-AC" and "AC-AC", are proposed for passing through the synchronous speed. The tested results show the feasibility of the proposed control technique, which sets a foundation for developing control technique of large size VSCF doubly fed wind generation system.
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