Research And Simulation For Low Voltage Ride-Through Of Doubly Fed Wind Power Generator

At present, the Double-Fed Induction Generator (DFIG) accounts for a large proportion in large-scale variable speed and constant frequency wind power generation System. With the increasing single-unit capacity and installed capacity of the DFIG unit, the interaction between the generator and grid becomes more and more important. This paper regards the DFIG as the research object and does deep study on the dynamic behavior of DFIG and low voltage ride through (LVRT) operation during grid voltage dip. The main contents are as follows:This paper derives the dynamic model of DFIG expressed in the reference reamer rotating in synchronous speed; the aerodynamic model, shaft system model and converter model of the wind turbines are presented. Based on this, the transient process of DFIG during grid voltage dip is analyzed; the dynamic responses of DFIG during two typical kinds of grid voltage dip are compared through simulation.The precise model of DFIG that the dynamic process of stator magnetizing current is considered is adopted. Based on stator flux oriented vector control theory, the LVRT control strategy of DFIG during grid voltage dip is proposed, including rotor converter controller and grid side converter controller. Simulation verifies the validity of the model and the feasibility of the control strategies.The active IGBT Crowbar circuit topology and the effect of the Crowbar circuit to the fault during grid voltage dip are analyzed. When severe grid voltage dip occurs, the use of active IGBT Crowbar can achieve LVRT of DFIG. The switching control strategy of Crowbar is researched detailed during simulation.The affect of DFIG that is caused by the asymmetric grid voltage is analyzed; according to the symmetric component method, the positive and negative sequence mathematical model of DFIG and the composition of active and reactive power and electromagnetic torque from the stator are derived. On the basis of which a current positive sequence component tracking control strategy is proposed and verified to be feasible through simulation.