Autonomous Control of Inverters in Microgrid

Grid-interactive inverters are mainly employed to optimize power injection while synchronizing with the grid's frequency and using the phase angle as the reference point. In certain circumstances, these inverters might be required to sustain power in an isolated grid segment. To achieve this, they need to generate reference points internally and collaboratively share the power load of the islanded segment, known as a microgrid. This article presents a self-governing control architecture for inverters that autonomously detect grid reconnection and islanding events, switching between grid-following (GFL) and grid-forming (GFM) modes without relying on data communication or supervisory controllers. The proposed control architecture employs a unique control-sync technique in which two sets of parallel control paths with minimal control loops are used for GFL and GFM modes of operations. Herein, while one set of control paths is engaged to generate the pulse-width modulated (PWM) signals, the other set synchronizes in the background. This ensures seamless transitions between GFL and GFM modes of operation. The efficacy of the proposed autonomous control scheme is validated through a hardware setup comprising a
$30\ \text{kVA}$
grid emulator and three 5–
$10\ \text{kVA}$
,
$208\ \text{V}$
three-phase inverters. The experiment results confirm that inverters with the proposed controller can detect grid reconnection and islanding events and autonomously switch between GFL and GFM modes.