Distributed Low-Frequency Oscillation Damping in Low-Voltage Islanded Multi-Bus Microgrids With Virtual Synchronous Generators

Abstract

In the low-voltage islanded multi-bus microgrid (LVIMB-MG), the virtual synchronous generators’ (VSGs’) inertia constant and damping coefficient play an important role in low-frequency oscillations (LFOs). However, existing LFO analyses lack the consideration of microgrids’ required rate of change of frequency (RoCoF) and steady-state active power-frequency (P-f) characteristics when designing the VSG’s inertia and damping. With these practical considerations, this paper reveals that the interactions between VSGs can cause significant LFOs, posing a threat to the microgrid’s stability. In contrast, the LFOs related to the interactions between SGs are less pronounced. To this end, a distributed LFO damping (DLFOD) control is proposed to suppress the LFOs between VSGs from two aspects: the adjustment of the VSG’s phase angle mitigates the uneven instantaneous active power sharing, while the adjustment of the VSG’s active power setpoint enhances the mutual damping. Compared with existing methods, the proposed DLFOD control 1) pertains to multi-bus microgrids, 2) guarantees the RoCoF and steady-state P-f characteristics, and 3) possesses a linear structure. Furthermore, a dynamic switching variable is devised to handle the disconnection and reconnection of communication links or VSGs, which enables the DLFOD control to remain partially functional during these interruptions. Finally, the proposed method is evaluated through theoretical analysis, real-time simulations, and experiments.