Simulation Research On Flexible Grid-Connection Of DFIG Wind Power Generation System

From the point of view of sustainable development, the fossil energy that the current human rely on will eventually be used up. To seek to som e new energy that can replace the trad itional way of generating has becom e a highest priority. As wind energy is an inexhaustible, clean and envi ronmentally friendly alternative energy sources that make wind power become the most mature, the largest development scale and the best way of generating commerc ial development a mong new ener gy power generation technology. Wind power has beco me the fastest growing green ener gy system and the fastest developing renewable energy sources.With the advance ment of wind power unit capacity and control technology enhanced, the wind power turn to be a grid connected la rge scale wind farm from distributed single wind farm. Wherein, the doubly-fed wind turbine become the wind energy resource developm ent in the field of a m ore advanced technology for its excellent operating characteristics and th e excitation frequency converter handling only slip power, which is a wide range of i ndustrial applications. This paper analyzes the characteristics of doubly fed wind power genera tion grid-connection at first, and focuses on the study of DFIG no-load grid-connection and load grid-connection which are suitable for Flexible Grid-Connection. At last the paper studies the conditions for grid connection and the transient process to deliver energy after the connection. Using the grid voltage and generator speed regula tion of rotor side excitation current to control the voltage of stator side accurately to make it in accordance with grid voltage. The paper put a m athematical model of doubly fed wind turbine firstly and then analyses the relationship between equivalent circuit and energy flow. According to the idea of coordinate transfor mation, the m athematical model of doubly fed induction generator in the static three-phase coordi nate system and the two-phase synchronous rotating coordinate syste m are deduced. Secondly, the rigid connection mode of synchronous wind generator and asynchronous wind generator and the flexible connection mode of doubly fed wind generator are anal yzed. When the wind power generation system adopts flexible grid connected mode, it can greatly reduce the harm to the power system when it is connected to the grid. Finally, this paper focuses on the analysis of the double fed wind power generation load and load control strategy. Both of the two grid connected m ode are both adopting stator flux oriented vector control technology and establishes DFIG stator flux observer. The DFIG no-load grid-connection adopts the roto r current single closed l oop control structure to calculate doubly fed motor reference stator flux by the grid voltage and to control the rotor current. The double fed wind power generation load grid connected strategy adopts voltage and current double closed loop control structure, and the outer loop is the stator voltage loop, and the inner loop is the rotor current loop. Compared with the no-load grid, besides collecti ng the grid voltage, the load grid connection also needs to collect the stato r voltage and stator curr ent. In this paper, the theory of con trol algorithm is sim ulated by Matlab/ simulink simulation, and the result shows that through the control algorithm de scribed in this paper, the impact current can be greatly reduced, and the “flexible connection” between the double fe d wind generator and the grid can be realized. The paper also designs th e software part of DFIG no-load grid-connection and load grid-connection,at the same time the flow chart of the program is given.