Small-Signal Modelling and Stability Analysis of Current-Controlled Virtual Synchronous Generators

Virtual Synchronous Generators (VSG), as an effective mean to improve the frequency and voltage regulation ability of the renewable power, had aroused wide concern. Researchers have proposed several VSG implementations, which can be classified into two categories: voltage-controlled VSG and current-controlled VSG. Voltage-controlled VSG have been extensively studied. However, few researches focused on current-controlled VSG. In this paper, we concentrated on the current-controlled VSG and its stability problem. Firstly, a small-signal model of current-controlled VSG was established to identify the oscillation modes of grid-connected VSG system. Moreover, the developed model was used to investigate damping characteristics of the system under various scenarios and with different control parameters. The results revealed that stability of VSG system was sufficiently impacted by virtual inertia and phase lock loop in VSG. Under some unfavourable conditions, current-controlled VSG would contribute to high-frequency or subsynchronous oscillation.