Control Strategy Of DFIG-based Wind Turbines For Power System Frequency Regulation

Wind power generation, as the most promising renewable energy, has beendeveloping rapidly in China. In order to better integration of wind turbines in powersystem and meet the increasingly strict wind farm codes, this paper presents asubject: Doubly fed Induction Generator-based wind turbine (DFIG) participation insystem frequency regulation. Thence, a comprehensive summary of the frequencycontrol strategies for DFIG has been conducted. This research will have a goodtheoretical and practical significance on the effective use of wind energy.(1) It gives the basics of doubly-fed wind power generation system, includingits operating principles, mathematical model of wind turbine and vector controlstrategy of DFIG. The operating range of wind turbine is divided into four zones,and each power tracking method belong to one area is described in detail. The2ndchapter has laid a good groundwork for frequency strategy designing later.(2) There are three kinds of frequency regulation method: inertial response ofsynchronous generator, primary frequency regulation and secondary frequencyregulation. The access to wind power has negative effects on frequency regulation,peak regulation and spare power capacity, bringing great challenge to the systemfrequency stability. The system frequency will fluctuate more severely with higherpenetration levels of wind power.(3) The fourth chapter analyzes the power control ability of DFIG, showinghow the additional output power of DFIG changes with the rotor speed; A conceptnamed controlled virtual inertia is put forward, and its mathematical formula isdeduced in detail. These illustrate that DFIG has the potential ability to participatein the system frequency regulation.(4) The author proposes two frequency control strategies of wind turbine:inertia control method by switching power tracking curves and primary frequency regulation by change of loading. The specific processes of two methods above areexplained in detail.(5) In Matlab/simulink, simulations have been conducted to validate frequencystrategies of DFIG. The results show DFIG with these strategies in this paper hasgood frequency response characteristics.