Doubly-fed Wind Power Generation System Control Strategy

It is of great significance to develop and utilize wind power, which is not only renewable but also without pollution when energy source scarcity and environment pollution are getting more and more serious. The wind power generation technology has become the research hotspot of many country's scholars. Wind power generation technique is improved greatly thanks to that more and more countries all over the world pay attention to it. With the increasing scale of wind power generation system, the investigation on wind power generation technique has been focused on improving the operation efficiency of wind power generation. For this reason, the technique of variable speed constant frequency (VSCF) operation which is capable of capturing the maxim wind power, becomes research hotspot. Doubly-fed induction generator and Permanent magnet Synchronous machine are commonly used in variable speed wind energy generation units above 1MW.With the operation and control of an Ac excited VSCF wind power generation system as the research subject, this dissertation made complete study by theoretical analysis and simulation. The main research contents include: the operation theory of doubly-fed induction generator (DFIG), the maxim wind power capture operation principle, reactive output power control of DFIG using direct torque control (DTC) technology, and the use of Direct Torque technology thinking, a new no-load grid-connection Control strategy is proposed.The main work of this paper: i) Using MATLAB / simulink establishment of a wind turbine model, wind speed model and the stator flux oriented vector control system of DFIG. Joint debugging the two models established a doubly-fed wind power control system mathematical model. Using MATLAB /simulink simulation platform, the doubly-fed wind power generation system from low wind speed to high wind speed operation process was studied, and torque observation and fuzzy control methods were achieving the greatest wind energy tracking.ii) Discussed how to achieve a direct torque control (DTC) for doubly-fed wind power system reactive regulation, and give a reasonable solution. In the MATLAB / simulink simulation platform, the simulation tests were done, and achieved a good simulation results.iii) With the single wind turbine capacity increases, the wind fields often are built in sparsely populated region, the end of a power supply network, the ability to withstand impact is relatively weak. when the wind field is connected to the grid , Power Grid will be quite big blows。In order to avoid this situation, appropriate grid connection technology is necessary. With the help of Direct Torque Control (DTC) technology thinking, a new no-load grid-connection Control strategy is proposed. DFIG rotor flux is adjusted to connect grid without overshoot current. Based on the theoretical study, a no-load grid-connection simulation model was then established and employed to make a comprehensive system simulation on the no-load operation before the grid-connection, the transient process at the cutting-in moment and the speed regulation after the cutting-in. The simulation studies prove that the proposed no-load grid-connection scheme is an relatively ideal cutting-in approach for the VSCF wind-power generation.