Research On Control Of The Converter Station Of VSC-HVDC For DFIG Wind Farm

In order to implement the basic national strategy for sustainable development, the wind energy has been devoted major effort to developing, while the development and utilization technique of wind energy get relatively mature. And the wind power generation system composed of doubly-fed induction generator(DFIG) which can realize variable speed constant frequency control has become more and more widely used, which improves the capture efficiency of wind energy and unit capacity. Nonetheless, the locations of the wind farm tend to be isolated, which are far away from the load center of big cities. Therefore the long-distance transmission and grid-connection of the wind energy are becoming more and more important. And as the development of the manufacturing technology of fully-controlled power electronic devices, the technology of high-voltage direct current transmission based on voltage source converter(VSC-HVDC) has been developed rapidly. It can realize decoupling control of active and reactive power. But the power fluctuations caused by the intermittent of the wind itself and the disturbance of grid itself may exercise an influence on the system reliability and stability, which has become the barrier to develop wind energy power. In order to improve the response to the fluctuations of wind energy power, it is necessary to study on control strategy of VSC-HVDC system with wind farm.Firstly, in this dissertation, the operation principle of DFIG under the vector control strategy of stator voltage-oriented was introduced. And the mathematical models of DFIG in the three-phase static coordinate system and two-phase synchronous rotating coordinate system were established, which achieves unit power factor at the double PWM converter and voltage stability at the dc bus, as well as the decoupling control of the active power and reactive power. Secondly, in the three-phase static coordinate system and two-phase synchronous rotating coordinate system, the mathematical model of VSC-HVDC system was established, and the operation characteristics of VSC-HVDC was analyzed, then the control strategy of VSC-HVDC system at the level of the converter station was discussed.For the sake of verification of correctness of the mathematical models and the control strategies obtained above, the DFIG and VSC-HVDC system with active network models are built via simulations in Matlab/Simulink separately, and the operation characteristics of DFIG and the vector control strategy were validated by the simulation results in chapter 2. Furthermore, fuzzy immune PID control method was applied to the inner current controller of the double closed loop structure in chapter 4, and the model was established in Matlab/Simulink. Compared with the conventional double closed-loop PI controller designed by the engineering setting method, simulation results showed that the designed controller got better tracking performance and anti-interference. Finally, with the DFIG in the wind farm, on the basis of chapter 2 and chapter 4, the model of VSC-HVDC system with wind farm was built in Matlab/Simulink. And the control strategy proposed in the chapter 4 was ameliorated with segmented control, in order to improve the waveform of power at the steady state. Then it had been carried on the simulation research, in order to verify the effectiveness of the control strategy designed above in the VSC-HVDC system with wind farm, which provided a solution and a certain reference value for engineering practice.