Research On Low Voltage Ride Through Of Wind Power System Based On DFIG

Doubly-fed induction generator system(DFIG) and Permanent magnet synchronous generator system were the mainstream of variable speed constant frequency(VSCF)wind power generation system,Doubly-fed wind power generation system with characteristics of low cost and high efficiency,could realize decoupling control of active and reactive power.Since the stator windings were directly connected to the grid,DFIG system were vulnerable to grid voltage sags. With the increased presence of wind energy in the electric power system, if the wind turbines were off-grid by a large scale, it would bring secondary impacts to the weakly grid which would lead to the entire grid voltage collapse.Therefore,it is very important to enhance the low voltage ride-through capacity of DFIG during the grid voltage sags fault.In order to enhance the LVRT ability of DFIQthe Crowbar circuit designed based on short current,from the viewpoint of magnetic linkage in the case of a three-phase short-circuit fault occurring at the terminal of DFIG,the analytical expression of the short-circuit rotor current were deduced together with the estimated expression.With the short current and grid-side converter withstand voltage, the series resistance range were deduced in crowbar circuit.Simulation results show that selecting the larger resistance in the setting range helps to accelerate transient current decay and improve the factor,which contribute DFIG system to restore normal operation.The traditional vector control were designed by Third-order model,which ignored the transient excitation current,the control effect is poor during voltage sags fault.In order to enhanced the LVRT capacity of DFIG system,combining vector control with the ADRC controller,the influences of disturbances on the wind energy generation system were estimated and compensated by the extended state observer. With PSCAD/EMTDC simulation platform,the dynamic process of DFIG system was simulated during the voltage sags fault.By comparing the traditional PID control、 improved control and ADRC control strategy,the results show that the ADRC control strategy owned the best performance,which helps to enhance the LVRT ability of DFIG.The vast grid reactive power would be absorbed by the crowbar-based doubly-fed induction generator (DFIG) wind turbine when grid voltage dip fault.The model of pitch control and STATCOM were built by analyzing the characteristics of DFIG system at grid fault.During the crowbar circuit active,the slip of DFIG could be restrained with pitch controller to reduce the amount of reactive power consumption.The grid side converter was switched to STATCOM operation mode to compensate reactive power of DFIG system. With PSCAD/EMTDC simulation platform,the dynamic process of DFIG system was simulated during the voltage sag.The simulation results show that the amount of reactive power absorbed by DFIG system from grid can be avoided with the proposed control strategy during voltage sag,which contributes to the recovery of the grid voltage.The effectiveness and correctness of the proposed control strategy are verified.