Impacts of Current Limiting on the Transient Stability of the Virtual Synchronous Generator

This article investigates the impacts of different current limiting strategies on the transient stability of the virtual synchronous generator (VSG). The power-angle curve of the VSG under different operating conditions is theoretically characterized in detail and experimentally verified through tests conducted on hardware-implemented lab-scale VSGs. It is shown that the reference current saturation approaches prioritizing the current vector angle, the d-axis current, and the q-axis current reshape the VSG power-angle curve in different ways. The resulting impacts on the VSG transient stability are comprehensively investigated through time-domain simulation of a battery energy storage system that is operated as a VSG and connected to a medium-voltage Canadian distribution feeder. The transient stability margin of the VSG is evaluated by determining the critical clearing time (CCT) of various fault scenarios. The studies conducted in the PSCAD/EMTDC software environment utilizing a detailed switching model of the VSG indicate that 1) the current limit of the VSG significantly impacts its power output during and after faults; and 2) the q-axis priority current limiting strategy provides a larger transient stability margin (CCT) as compared with the current vector angle and d-axis current priority approaches.