Analysis and Mitigation of Oscillatory Instabilities Between GFM-VSG and DOL-IML in Islanded Microgrids

Islanded converter-based microgrids dominated by direct-on-line induction motor loads (DOL-IMLs) are particularly prone to low-frequency oscillations (LFO), which can threaten system stability and result in economic losses if unaddressed. Despite the critical implications of this issue, its fundamental causes remain relatively under-explored in the existing literature. This paper identifies the underlying causes of this issue by performing a small-signal analysis of an islanded IML-dominated microgrid powered by grid-forming virtual synchronous generators (GFM-VSGs) and grid-following (GFL) converters. Furthermore, the effects of different system parameters such as line impedance, GFM-VSG's voltage control loop bandwidth, virtual impedance, and IML torque are examined. Finally, recommended ranges for key system parameters are provided to suppress the observed LFO.