Study On Three-phase Short-circuit Protection Characteristics Of Doubly Fed Induction Generator

With a wide range of applications of megawatt wind turbines, three-phase short-circuit protection has become research priorities of VSCF DFIG Three-phase short-circuit of DFIG will lead to a series of transient problems of wind power generation system, such as the rotor side over current, which will cause the converter fails, and the impact of the electromagnetic torque adversely affect the transmission mechanism, therefore it must be short-circuit protection of DFIG.In order to facilitate the study of three-phase short-circuit characteristics of DFIG, based on the operating characteristics of wind turbine and DFIG, establish dynamic mathematical model of DFIG. When DFIG three-phase short, for the inrush currents moment, generator speed has no obvious change, so the analysis does not consider the changes in speed, and short circuit analysis can be simplified as electromagnetic transient problems. Three-phase short-circuit transient process can look as a superposition of steady state operation and processing the operating status of the reverse voltage. We can solve short-circuit current and torque by using the Laplace transform and inverse transform, it reveals impact various components relative to the short-circuit process, and then we propose the three-phase short-circuit protection of DFIG. Through the research of Crowbar circuit, the maximum resistance of fast short-circuits protection devices retune; by analyzing of the rotor excitation voltage and the study of controlling the rotor side of the excitation voltage, so as to protect the three-phase short-circuit of DFIG.On the basis of theoretical analysis, based on Matlab/Simulink simulation platform, we can build DFIG three-phase short-circuit simulation model. By simulation analysis and comparison of rotor side with different setting values when DFIG three-phase short circuits, the setting value proposed by this article effectively suppresses the rotor current, and protects the converter; simulation analysis and comparison of controlling different rotor excitation voltages, the rotor-side excitation control voltage proposed by this article can effectively reduce the short circuit current, so as to achieve the purpose of protecting the rotor-side converter.