چكيده به لاتين
Nowdays, doubly fed induction generators (DFIGs) are widely used in wind power plants, due to their advantages such as ability to control active and reactive power, lower converter cost, reduced mechanical stress and improved efficiency. Nevertheless, the direct connection of the DFIGs stator to the grid has made them very sensitive to grid disturbances. Current grid codes require DFIGs to stay connected to the grid during grid fault. The fault ride through (FRT) capability of DFIGs is the focus of this thesis, in which modification to the DFIG controller have been proposed to improve the FRT capability. In this thesis, the behavior of DFIG during fault condition has been surveyed and the effective control strategy in order to improve FRT is proposed. This scheme contains the active control and passive control. The active control has been proposed by use of model predictive control (MPC) in order to reduce the inductance over voltages in rotor. The passive control includes resistors series with the rotor, which is used to decrease rotor’s over current in deep voltage sags. Transitional state of the system under fault condition is improved by use of the proposed method. The negative results of the fault on the system include rotor’s over current, oscillation of electromagnetic torque and DC link’s over voltage decrease and the effectiveness of the system increase. The simulation of the dynamic behaviour of DFIG-based wind turbines during grid fault is simulated using MATLAB/Simulink. The results obtained clearly demonstrate the efficacy of the proposed method.
Keywords: Wind Turbine, Double Fed Induction Generator, Fault Ride Through Capability, Model Predictive Control.
