Soft Grid Connection of Cascaded Doubly Fed Induction Generator Using Direct Torque & Flux Control for Wind Turbine Application

A modified direct torque control (DTC) method is proposed for grid connection of Cascaded Doubly Fed Induction Generator (CDFIG) used in wind turbine. The presented method and its dynamic model is obtained in stator reference frame of control machine. To achieve a voltage in the stator of power machine with equal amplitude and matched phase and frequency to the grid voltage, the magnitude and frequency of stator flux is controlled respectively by two PI controllers. The inner control loops utilize hysteresis controller and pre-defined look-up table to track the reference values. The proposed control method has high performance, i.e., grid connection with zero overcurrent and fast dynamic response, during the CDFIG loading. The experimental results on a 3 kW CDFIG reveals the proposed method effectiveness for grid connection of CDFIG.