Real-time sliding mode control for a doubly fed induction generator

This paper proposes a control scheme based on the block control technique using sliding modes, for a doubly fed induction generator (DFIG) prototype connected to an infinity bus. The DFIG is widely used as a wind generator; it allows the rotor speed to vary while synchronizing the stator directly to a fixed frequency power system. The generation scheme for the DFIG has one back-to-back PWM voltage-source converter connected between the rotor and the electrical grid. The rotor side converter (RSC) is connected via a dc link to the grid side converter (GSC), which is in turn connected to the stator terminals directly or through a step-up transformer. A block control scheme for the RSC is proposed to control the electric torque and the reactive power independently. The variables to be controlled by the GSC are the dc voltage in the dc link and the reactive power in the step-up terminals. The performance of the control scheme proposed is illustrated via real-time implementation in a 1/4HP DFIG prototype.