Research On Control Strategy Of Doubly-fed Induction Generator When The Grid Voltage Unsummetrical Swells

Wind power generation is playing a vital role in the world’s new-energy consumption in this era. Countries around the world are paying more attention on the research of wind power generation nowadays under the current background of fossil-energy shortage. At present, the low voltage ride through (LVRT) technologies of doubly-fed induction generator(DFIG) tend to be mature. However, the influences of grid voltages swell on wind energy conversion system(WECS) and the high voltage ride through (HVRT) technologies of DFIG have not attracted enough attention. Therefore, this article studies the HVRT control strategy of DFIG control system.Firstly the transient mathematical model of the WECS under the grid voltages unsummetrical swell is deduced to pave the theoretical way for the design of the control system in this article.An effective PLL is of great importance to vector control. The basic principle of angular-frequency-locked and phased-locked loop based dual second-order generalized integrator is detailed. Then a dc-component self-adapting compensation unit is inserted into the SOGI to enhance the immunity of dc-component caused by sampling.In order to enhance the reliability of the grid-side control system, reactive power and dc-capacitor current closed loops are designed to suppress the fluctuations of reactive power and bus dc-voltage respectively.Considering the line inductive reactance, this paper analyzes the positive and negative sequence reactive current assignment of the rotor-side converter and discusses the effects of stator-side positive and negative reactive current on the terminal voltage support, the unbalance factor and the pulsating stator reactive power. A flexible positive and negative sequence voltage closed-loop control strategy of reactive power optimization is designed when the grid voltages unsymmetrical swell.Simulations and experiments prove the feasibility and effectiveness of the control strategies mentioned above.