A control scheme for mitigation of DFIG oscillatory behavior related to FIDVR problem

This paper proposes a control scheme for the grid-side converter (GSC) of the doubly fed induction generator (DFIG) in order to mitigate the oscillatory effect of the generator speed caused by the problem of Fault Induced Delayed Voltage Recovery (FIDVR). In this scheme, the mode of control changes the reference of the current of the GSC to the DFIG contribute with the injection of reactive power to the grid. The FIDVR problem is caused by the presence of induction motors in the system. The DFIG is connected to the distribution system operating under unbalanced conditions. Several conditions of load imbalance were used to evaluate the effect of the imbalance in the oscillations of the DFIG comparing the results between balanced and unbalanced conditions. It was observed that the presence of the negative sequence component of the electromagnetic torque of the motor, due to operation of unbalanced conditions, causes the net torque to be smaller (when compared to the balanced case) and consequently it takes longer for the motor to reach the steady-state. This effect has impact on the oscillatory behavior of the DFIG reducing the damping of the electromechanical oscillations. The damping and the frequency of the oscillations are obtained by the Prony method. The results showed that the increase in the percentage of load unbalance causes a change in the damping of the oscillations of the DFIG. The proposed control scheme was capable of reducing oscillatory behavior of the DFIG and increase the damping of the electromechanical oscillations of the generator.