Comparative Studies on Damping Control Strategies for Virtual Synchronous Generators

Virtual synchronous generator (VSG) control is found to be effective solutions to address the low inertia issue caused by the high penetration of inverter-based resources. However, the active power oscillation is introduced as a side effect due to the second order oscillation characteristics of VSG. At present, various methods have been proposed to damp the active power oscillation by means of feedback or feedforward. In this paper, a comprehensive comparative study is conducted to identify the merits and drawbacks of existing damping methods from the perspectives of dynamic performances and the rate of change of frequency (RoCoF). The results indicate that the power reference feedforward (PRFF) based method is capable of adjusting the dynamics of VSG to any desired level under power reference change, without affecting the original inertia characteristics. However, its performance cannot be guaranteed under the grid frequency variation. Therefore, a further improvement is proposed in this paper by adding a grid frequency feedforward to PRFF, which leads to a two degree of freedom (2DOF) control structure. The 2DOF control structure enables the designer to independently adjust the dynamic responses of VSG under the disturbances of the active power reference and the grid frequency, without degradation of the original inertia response of VSG. The effectiveness and merits of the improved method are proved by hardware in the loop tests.