An improved control strategy of DFIG systems
An Improved Control Strategy for DFIG System and
Dynamic Voltage Restorer under Grid Voltage Dip
Peng Cheng, Heng Nian, Member, IEEE
College of Electrical Engineering, Zhejiang University, Hangzhou, China cheng_peng@zju.edu.cn Abstract：With the increasing percentage of wind power in the utility grid, grid codes require that wind turbines must have low voltage ride through (LVRT) capability. Considering that doubly fed induction generation (DFIG) systems have the tolerance capability , to overcome the drawback of LVRT operation of DFIG system using crowbar, a dynamic voltage restorer (DVR) is connected to the stator side to prevent the stator voltage fast changing, and then the rotor side converter
(RSC) can be in normal operation. A mathematical model of the rotor voltage of DFIG during a symmetrical voltage dip is presented to describe the allowable changing rate of the stator voltage. A new connection structure of DVR is proposed where
DVR and GSC share a DC capacitor. Based on the coordinated control of the DFIG system and DVR, the active power regulation and reactive power compensation can be implemented under the grid fault. The simulation results for a 1.5MW DFIG system is given to show the effectiveness of the proposed protection compared to the rotor crowbar during grid fault.
fault, the RSC can be disconnected from the rotor winding and the crowbar is connected to the rotor winding, in which operation the DFIG behaves as a squirrel cage induction motor with a larger slip. However, the drawback of this method is that the rotor is out of control as soon as the rotor crowbar is inserted and a great amount of reactive power is absorbed which can further reduce the grid voltage and then even lead to the collapse of the grid. At the same time, the peak of torque cannot be eliminated by the rotor crowbar and more mechanical stresses are shared by the driver shaft and the gear box. Therefore, although the rotor crowbar can limit
Dynamic Voltage Restorer under Grid Voltage Dip
Peng Cheng, Heng Nian, Member, IEEE
College of Electrical Engineering, Zhejiang University, Hangzhou, China cheng_peng@zju.edu.cn Abstract：With the increasing percentage of wind power in the utility grid, grid codes require that wind turbines must have low voltage ride through (LVRT) capability. Considering that doubly fed induction generation (DFIG) systems have the tolerance capability , to overcome the drawback of LVRT operation of DFIG system using crowbar, a dynamic voltage restorer (DVR) is connected to the stator side to prevent the stator voltage fast changing, and then the rotor side converter
(RSC) can be in normal operation. A mathematical model of the rotor voltage of DFIG during a symmetrical voltage dip is presented to describe the allowable changing rate of the stator voltage. A new connection structure of DVR is proposed where
DVR and GSC share a DC capacitor. Based on the coordinated control of the DFIG system and DVR, the active power regulation and reactive power compensation can be implemented under the grid fault. The simulation results for a 1.5MW DFIG system is given to show the effectiveness of the proposed protection compared to the rotor crowbar during grid fault.
fault, the RSC can be disconnected from the rotor winding and the crowbar is connected to the rotor winding, in which operation the DFIG behaves as a squirrel cage induction motor with a larger slip. However, the drawback of this method is that the rotor is out of control as soon as the rotor crowbar is inserted and a great amount of reactive power is absorbed which can further reduce the grid voltage and then even lead to the collapse of the grid. At the same time, the peak of torque cannot be eliminated by the rotor crowbar and more mechanical stresses are shared by the driver shaft and the gear box. Therefore, although the rotor crowbar can limit