Study On Power Control Technique For VSCF Doubly-fed Wind Power Generation System

In nowadays, fossil energy is being exhausted and environment is polluted more and more seriously, so the development and use of renewable energy are imposed great significance to sustainable development. Wind energy, with its advantages of rich resource, easy development and high cost-effective, are given more and more attention.With the improvement of wind power technology, ensuring the reliable and stable operation of wind power system is no longer a problem. On the one hand, wind energy has the characteristics of randomness and instability, which will cause the output power of wind turbine varying with the change of wind speed. And the power fluctuations may lead serious impact to the power quality of gird. On the other hand, because of the huge amount of manufacture costs and expensive maintenance costs, the wind power system is demanded to have a higher efficiency and generating more power in its limited life. So the effective power control methods are hoped in wind power system to improve the power quality and increase the generation efficiency. The variable speed constant frequency (VSCF) doubly-fed wind power generation system, the most popular type, is as to the research object in this paper, and its power control techniques are given comprehensive and depth study.First, the stator flux vector control of doubly-fed induction generator (DFIG) is used to implement the decoupling of active power and reactive power, which make the subsequent optimization control of active power and reactive power have its value. Then the optimization control strategy of active power and reactive power is researched based on fuzzy control theory, respectively. At the low wind speed region, the power increment, speed increment of wind turbine and the wind speed change information are used as input variables to design the optimal speed fuzzy controller, which can have a good maximum power point tracking(MPPT) performance both in wind speed stable and change state. At high wind speed region, the variable field fuzzy pitch controller is designed with good static, dynamic performance and strong robustness, which can solve the problems of traditional PID controller and conventional fuzzy controller in pitch control perfectly. After analyzing the reactive power and loss characteristic of DFIG, the loss increment and stator reactive power increment of DFIG are used as input variables to design the optimal reactive power fuzzy controller, which can implement the minimum loss operation of DFIG by regulating stator reactive power. Finally, the simulation models of VSCF doubly-fed wind power system are built in MATLAB/SIMULINK toolbox. The validity and effectiveness of each control strategy mentioned are verified respectively by simulation experiments.