Sensorless Vector Control for Grid Synchronization of Doubly-Fed Induction Generators

Wind turbine systems (WTSs) based on a doubly-fed induction generator (DFIG) are widely used in the wind power industry. In the DFIG topology, the stator winding is directly connected to the grid. This topology requires some caution during grid synchronization to avoid undesired overcurrent. In this context, this paper proposes a new control strategy to improve the connection of the DFIG to the grid. An augmented state and disturbance observer estimates the direct and quadrature components of the stator voltage. These components are used to ensure soft and fast synchronization of the DFIG to the grid. This can be achieved by controlling the rotor current in a synchronous reference frame to adjust the open-circuit stator voltage to follow the grid voltage. Numerical simulation and hardware implementation results verify the efficiency and effectiveness of the proposed control scheme.