Modified Voltage and Frequency Control of Parallel-Connected Grid-Forming Inverters by Virtual Synchronous Machine Controller

Abstract

With higher penetration of Distributed Energy Resources (DERs) into the utility power grid, the power control architecture of the grid must be revisited. The main reason for this is that DERs mostly interface with the grid through power electronics (i.e. inverters), whereas traditional centralized grid-forming has been majorly achieved by Synchronous Generators (SG). By employing a Virtual Synchronous Machine (VISMA) controller, benefits such as communication-less and independent power control can be achieved concurrently with maintaining power grid standards (stable voltage and frequency constraints). However, the VISMA controller cannot operate under conditions where the central grid is absent, especially for the black-start condition. In this paper, a modified VISMA (called Mod-Visma) is proposed, which incorporates the missing voltage and frequency regulation outer loops into the baseline VISMA control architecture. The performance of this modified controller is validated in MATLAB/Simulink.