Distinct Low-Frequency Roles of Virtual Resistance and Active-Power Damping Coefficient in VSGs

Abstract

Virtual synchronous generator (VSG) control is widely used to support the stable integration of converter-interfaced renewable generation. The active-power damping coefficient Dp and constant virtual resistance Rv tune VSG oscillations through the swing equation and the converter electrical port, respectively. However, their mechanisms and effects on the low-frequency mode dominated by the active power control (APC) loop remain unclear. This paper develops a small-signal model with Rv and uses an equivalent second-order model to analyze the torque mechanisms and modal effects. The results show that increasing Dp enhances the damping torque, moves the dominant underdamped poles to the left, and reduces the magnitude of their imaginary parts, thereby increasing the modal decay rate and lowering the oscillation frequency. In contrast, increasing Rv weakens the synchronizing torque and moves the poles mainly toward the real axis, lowering the oscillation frequency with little change in the modal decay rate. Thus, although both parameters can be tuned to improve the oscillatory response, they act through different low-frequency mechanisms and affect the dominant mode differently. Simulation results validate the theoretical analysis.