PI Control Loop–Based Frequency Smoothing of a Doubly-Fed Induction Generator

This paper proposes a frequency-smoothing scheme of a doubly-fed induction generator (DFIG) that can significantly eliminate the frequency fluctuations caused by continuously fluctuating wind speeds. To achieve this, a proportional-integral (PI) control loop depending on the frequency deviation instead of a proportional control loop used in conventional schemes is added to the maximum power point tracking loop. The P control loop in the proposed frequency-smoothing scheme eliminates the alternating component in the frequency deviation, whereas the I control loop eliminates the slowly-varying component. The gains for the P control loop and I control loop are suggested for effectively using the rotating masses of a DFIG while avoiding over-deceleration of the rotor speed. The simulation results evidently demonstrate that the proposed scheme nearly removes the frequency deviation under various wind conditions, by using the proposed PI control loop, especially in high penetration levels of wind.