Research On Doubly-fed Wind Power Generator And Its Control System

Continuous consumption of energy and environmental deterioration have become an increasingly common topic of concern to countries in the world. Wind energy is a kind of clean and renewable energy which has caught great attention from various countries in the world. The rapid development of wind power technology, led to the rapid prosperity of wind power industry. The wind power generation technology has developed to the present megawatt variable speed constant frequency (VSCF) from constant speed constant frequency (CSCF). The VSCF double fed induction generator (DFIG) has many advantages such as variable speed generation, four-quadrant power flow control, improved power quality, small converter capacity and it has come into wide use in wind power system.The basic structure, operation principle and energy flow of DFIG are analyzed and the mathematical model of DFIG is established, based on which the control system of rotor-side and grid-side converters are set up. The stator flux-oriented vector control is adopted for rotor-side converter. Then, the output of active and reactive power can be regulated respectively. The grid-side converter adopts grid voltage oriented vector control to realize DC voltage stability and grid-side unity power factor control. Introduce the concept of low-voltage ride-through (LVRT) and Chinese LVRT standard of wind power generation system. Derived the DFIG model detailedly, which has take the changes of gird voltage into account, and gives the corresponding improvement of the control strategy.In this paper, by taking the use of Matlab/Simulink as a software platform, we implement a simulation study of the DFIG. The established model and the model in library of Matlab/Simulink have been integrated in simulation research. The whole process simulation including grid connection, control strategy switch and power generation shows that DFIG can meet grid connection condition quickly with the control strategy and is connected to grid with no current shock nearly. The maximum wind energy capture is realized and the output of active and reactive power can be regulated respectively. In the condition of the grid voltage dips, by combining the improved control strategy and the Crowbar protect circuit, the control target of the LVRT goal can be achieved.