An Integrated Control of Enhanced-PLL and Synchronverter for Unbalanced Grid

Abstract

Synchronverter (SV) control is a popular control for distributed energy resources (DERs), as it has the capability of synchronous generator (SG) behaviour emulation. However, additional control along with a higher order phase-locked loop (PLL) must be integrated to SV control, for ripple free power injection into an unbalanced grid. Thus, the enhanced-PLL (EPLL) structure comprising of positive, negative and zero sequence core units, is integrated to standard SV control in the proposed control, which is capable of ripple free power injection by DER into an unbalanced grid. Further, the proposed integrated control is also capable of successfully achieving pre-synchronization i.e., synchronization of DER voltage to the grid voltage, before connection of DER to the grid. Other important benefits of proposed control over existing VSG methods for unbalance grid condition, are reduced number of parameters design due to the simple modular control structure and usage of inherent low pass filter of SV in the positive sequence core unit. Simulation results demonstrating successful pre-synchronization and ripple free power injection by DER into an unbalanced grid are presented in this work.