Virtual Shaft Control of DFIG-Based Wind Turbines for Power Oscillation Suppression

The flexible shaft coupled to the synchronous generator (SG) is critical for the doubly-fed induction generators (DFIG) based wind turbines to improve the ability to suppress system power oscillations. The rigid shaft coupling relationship between the DFIG and SG is analyzed first under the current virtual synchronous generator (VSG) control. To give the power system a vibrational degree of freedom, a novel virtual shaft is added to the VSG emulated by the DFIG-based wind turbine. The power system's two-degree-of-freedom (TDOF) coupled motion model with VSG is then established. The virtual shaft coupling adapted to a DFIG is designed using anti-resonance theory, and the amplitude-frequency characteristic of the TDOF power system is analyzed. With the additional stiffness of the virtual shaft, the power support functions of the VSG, including inertia and damping, are integrated by optimizing the oscillation amplitude at two fixed points in the frequency domain. Finally, on a controller hardware-in-the-loop platform, a typical power system with a high penetration of wind power generation is simulated. The test results demonstrate that by employing virtual shaft coupling, it is possible to suppress system frequency variation and rotor angle oscillation during transient events, significantly improving the reliability of the power support provided by wind turbines.