An Additional Damping Torque Method for Low-Frequency Stability Enhancement of Virtual Synchronous Generators

Low-frequency oscillations may occur in a virtual synchronous generator (VSG), resulting from an insufficient equivalent damping ration, which may be a serious stability issue for VSG. Thus, an additional damping ration is expected to be provided without affecting droop behaviors and the inertia response of VSG. To that end, an analytical approach based on combining a damping torque model and a small-signal model is developed to investigate the damping behaviors of the VSG. The relationship between the two models is brought to light, indicating that the damping torque model is suitable for qualitative analysis to give the contribution of different feedback loops to the system damping level. Subsequently, the latter is adopted for quantitative analysis to illustrate the damping ration of the system. Furthermore, an additional damping torque method is proposed, which can provide an extra damping ration for the system by increasing the equivalent positive damping torque and guaranteeing that the original droop characteristics and inertia are not compromised. Besides, the proposed control method is implemented by inserting an auxiliary branch into the power control loops of VSG. Experimental results verify the theoretical analysis and the effectiveness of the proposed additional damping method.