Virtual Shaft Control of Virtual Synchronous Generator With Nonlinear Stiffness for Power Oscillation Suppression

Efficient power oscillation suppression in broad bandwidth and reduction of self-induced resonance risk are critical for the wide application of the virtual synchronous generator (VSG) in power systems with a high penetration of wind power generation. In this paper, the linear virtual shaft coupling relationship between the VSG emulated by the doubly fed induction generator (DFIG)-based wind turbine and synchronous generator (SG) is analyzed firstly. The two degrees of freedom model of the power system with the VSG is then established under the application of the virtual shaft to connect the generators. A novel virtual shaft with cubic stiffness is then introduced to the reduce the self-induced resonance risk of the VSGs. Using the optimal bandwidth theory, the oscillation suppression bandwidth of the VSG with the nonlinear virtual shaft are extended. To further improve the power support functions of the VSGs, a novel nonlinear virtual shaft control adapted to the DFIG-based wind turbine is proposed, and the design parameters are optimized. Finally, a typical 9-nodes power system with a high wind penetration of 32% is simulated on a controller hardware-in-the-loop platform. The test results demonstrate that the nonlinear virtual shaft reduces the risk of resonances by extending the oscillation suppression bandwidth of the VSG, thus improving the power support ability of wind turbines for system frequency regulation and power oscillation suppression.