Enhanced Compensation Filter to Mitigate Subsynchronous Oscillations in Series-Compensated DFIG-Based Wind Farms

This paper presents a control strategy to mitigate subsynchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based wind farms integrated into series-compensated transmission systems. The strategy has two parts: in the first one, a compensation filter based on the motion-induction amplification concept is proposed to increase the damping of the DFIG machine in the subsynchronous frequency range; in the second one, a proportional-integral (PI)-like controller is designed using an optimal quadratic technique to minimize the control effort and the additional rotor voltage required by the SSO damping action. The SSO mitigation strategy acts locally on the DFIG control system reducing the negative resistance the rotating machine presents to the grid at subsynchronous frequencies; this approach reduces the control dependence on the topology and resonance frequencies of the network. The control strategy is validated with a case study based on the Argentinian power system and evaluated in a wide range of operating conditions, showing that the DFIG control system can be enhanced to mitigate poorly damped SSOs and increase the penetration level of wind power in the system.