Small Signal Analysis of Rotating Reference Frame Based Synchronization Control for Microgrid to Grid Changeover

Reliable synchronization is essential for ensuring stability during the transition of microgrids between islanded and grid-connected operation, particularly in converter-dominated lowinertia systems. This paper outlines a small signal analysis for the novel synchronization control of an islanded microgrid comprising two or more parallel-connected voltage source converters. It focuses on the development of simple and effective microgrid synchronization strategies with a minimum Rate of Change of Frequency (ROCOF), enabling the integration of Distributed Energy Resources (DER) into growing low-inertia power systems. The proposed method is based on a rotating reference frame-based algorithm with two Proportional-Integrator (PI) controllers at the secondary control level, minimizing the computational complexity by reducing the number of control loops compared with conventional approaches. A small-signal model has been developed and validated using eigenvalue analysis to ensure stability during the mode transitions. The developed controls were validated on a test setup comprising of a 25 kW Grid-Forming Converter (GFC) and a 25 kW Grid-Following Converter (GFL).