Research On Wind Generator Excitation Adjustment And Low Voltage-ride Through Technology Of Wind Turbine

As a kind of clean and renewable energy utilization, wind power generation has experienced rapid growth in recent years in the world. With the rapidly increase of wind power generation capacity, its influence on grid is becoming more and more remarkable.The double-fed induction generator(DFIG) has the benefit of variable speed constant frequency operation, active and reactive power independent adjustment, low converter capacity. So it becomes the mainstream type of wind generator. But, it has deficiencies in coping with power grid failure. The voltage sag is the most important fault which caused by short circuit or open circuit. When voltage sag deeply, it brings great threaten to the wind turbine safety and grid stability. As a result, improving low voltage ride through(LVRT) ability has became a hot topic. In this paper, on the basis of grid code from different countries, a research has been made to improve low voltage ride through ability of double-fed wind turbines.Firstly, doubly-fed wind turbines and the low voltage ride through technology requirements are briefly introduced to point out the differences among DFIG, synchronous generator and induction generator, and the basic principles of double-fed motor VSCF(variable speed constant frequency) operation are analyzed as well. Secondly, the mathematical models of DFIG and the converter are built. This paper also briefly introduces both fluxed-oriented control strategy of the rotor side and grid voltage oriented control strategy of the grid side converter when DFIG units operate steadily. Then, DFIG operation is simulated with the tool of Matlab/Simulink and transient electromagnetic relations are analyzed to explain the transient physical process of DFIG. based on the understanding of the generator transient physical process when grid short-circuit fault occurs, the new excitation control strategy which is aimed at making DFIG dose not run off the grid when grid faults happen is introduced. Simulation comparing the LVRT ability of these two strategies is done by Matlab/Simulink. The new excitation control strategy's validity is verified, which provides a theoretical basis for doubly-fed wind turbines'LVRT. Finally, applying the crowbar circuit when large value of the grid voltage drops is discussed. Bypass rotor side converter is used to protect wind turbines from damages when large value of the grid voltage drops, and it is verified by simulation.