Impact of Voltage Close Loop Control on Small Signal Stability of Virtual Synchronous Generators

Abstract

Virtual Synchronous Generators (VSG), as an effective mean to improve the frequency and voltage regulation ability of the photovoltaic (PV) power generation, had aroused wide concern. Different PV-VSG control structures had been conducted in existing researches. One significant distinction between various VSG control structures was whether voltage close loop control (VCLC) was contained in VSG control system or not. To study the impact of VCLC on PV-VSG stability, this paper developed the small-signal models of PV VSGs with and without VCLC. The oscillation modes of both VSGs were calculated based on the developed models, which were applied to investigate the influence from VCLC on VSG damping characteristics as well. On the basis of that, the impact of VCLC on the adaptation and frequency regulation ability of VSG were analyzed. The results indicated that if PV VSG was connected to a low voltage or a weak power grid, the implementing of VCLC was benefit for the oscillation modal characteristics of PV VSG.