Enhancing the performance of grid synchronization in DFIG-based wind turbine under unbalanced grid conditions

Abstract

Grid synchronization has always been a major challenge for grid-connected converters when the grid voltage is unbalance. Hence, this paper proposes an improved synchronize method for DFIG generator connected to an unbalance grid. In the proposed method, the stator voltage is directly controlled in order to follow the grid voltage. The grid voltage is divided into positive and negative components, and each one is entered in a separate control loops to observe the unbalanced grid voltage in the stator. Then, the stator voltage precisely follows the grid voltage. The rotor current is also applied in the inner control loop to control the rotor current before and after synchronization. The proposed method is tested on a 100 kW DFIG prototype; simulation and experimental results show that this improved control method works well with a fast response time and the DFIG stator voltage follows the grid voltage accurately under unbalanced conditions.