Analysis and Mitigation of Electromechanical Oscillations for DFIG Wind Turbines Involved in Fast Frequency Response

This paper is committed to developing a thorough analysis on the electromechanical oscillations (EOs) of doubly-fed induction generator (DFIG) wind turbines (WTs), taking into consideration the implemented frequency control and drivetrain dynamics of the mechanical system. Some basic recommendations for mitigating EOs would be hence attained. To this end, a linearized model of DFIG WT is proposed to present the interplay between frequency control and the dynamics of WT's drivetrain and electrical system. Then, the conventional torque analysis method is used to establish the basic effects of the frequency control on the damping of the drivetrain and electrical system frequency dynamics. Therein, the adverse effects could incur detrimental EOs, viz., drivetrain torsional oscillations (TOs) and electrical system low-frequency oscillations (LFOs). To mitigate such TOs and LFOs, this paper proceeds with an investigation of different alternatives to stabilize the torsional dynamics of drivetrain and the frequency dynamics of electrical system, meanwhile, to minimize undesired impacts caused by their interactions. Simulation studies on two test systems validate: the basic concepts obtained from theoretical analysis and that the findings can be generalized to multi-machine systems.