A Modified Dual Loop Droop Control for Parallel Operation of Grid-forming Converters

Distributed Generators (DGs) are becoming more integrated into the existing power system due to the growing popularity of renewable energy sources. However, in contrast to synchronous generators in a conventional power system, most renewable-based DGs are connected to the grid via a low inertial power electronic interface, which can impact the system stability significantly due to their uncertain generation. These power electronic converters can operate in grid following or grid forming mode. However, the latter taxonomy is the most widely used topology since it can operate in grid-connected or standalone modes and can self-restore the nominal frequency and voltage conditions. This article presents a modified dual loop droop control technique to operate two grid-forming converters in parallel, acquire precise power sharing, and maintain voltage regulation according to the DGs' rated capacities. The mathematical formulation and the simulation of the proposed control strategy are performed in MATLAB/Simulink, while OPAL-RT is utilized for the real-time digital simulation of the framework in Software in loop (SIL) mode.