Analysis of Synchronverter Control with Virtual Impedance during Grid Voltage Variations

Synchronverter (SV) or virtual synchronous generator (VSG) control is a popular control for distributed energy resources (DERs), as it has the capability of synchronous generator (SG) behaviour emulation. For the configuration of standard SV controlled (DERs) connected to grid, step variations in amplitude of grid voltage within normal range leads to transients in current. Earlier works regarding virtual impedance show that their implementation to VSG or SV controlled DERs has some capability of current transient reduction during grid voltage variations. However, there is no detailed analysis regarding suppression of current transients and effect of virtual impedance on system stability. Hence, this paper focuses on these analysis by obtaining a complete small signal model of the grid connected DER configuration and control. Through relevant magnitude bode plots from the small signal model, analysis of current transients suppression is discussed. Further, the effect of high virtual impedance on system stability is discussed based on eigenvalue analysis and simulation results are given to validate the analysis presented in this paper.