A Strategy to Eliminate Instantaneous Active Power Oscillations and Reduce High Currents in the DFIG During Asymmetric Voltage Sags

Abstract

Wind turbines are widespread around the globe, and the number of windfarms connected to the grid is continually increasing. The Doubly-Fed Induction Generator (DFIG) plays an important role, since it is one of the most used configurations for wind power generation. DFIG-based wind plants, however, are very sensitive to grid disturbances, specially to voltage sags, as these machines have their stator circuit directly connected to the grid. Voltage sags can result in oscillations in active power, torque and DC link voltage, as well as damage the machine and the back-to-back converter due to high currents that arise in such type of contingency. This work proposes a control strategy applied to the rotor-side converter (RSC) of the DFIG, in order to protect the machine and the back-to-back converter during voltage sags. The aim of the control strategy is to reduce the machine currents and also to remove the oscillating active power caused by unbalanced voltage sags.