Control of DFIG using Back-To-Back PWM Converters

The studied system here is a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG). The stator of the generator is directly connected to the grid while the rotor is connected through a back-to-back converter which is dimensioned to stand only a fraction of the generator rated power. In order to improve the operation capacity of wind turbine under critical situation, the intensive study of both machine side converter control and grid side converter control is necessary. The system uses two back-to-back converters in the rotor circuit. The basic concept behind the total system (DFIG with back to- back converters) is that the machine-side converter controls the active and reactive power by controlling the d-q components of rotor current (i.e. idr and iqr), while the grid-side converter controls the dc-link voltage and ensures the operation at unity power factor by making the reactive power drawn by the system from the utility grid to zero.