Analysis and Mitigation of Low-Frequency Interactions Between the Source and Load Virtual Synchronous Machine in an Islanded Microgrid

Source-side virtual synchronous machines (VSGs) and load-side VSMs (LVSM) are gradually utilized together in the microgrid to provide virtual inertia and damping. However, instability occurs in the islanded microgrid system due to the interaction dynamics between the VSG and the LVSM, which has been investigated in this article. At first, the dq-frame impedance models of the VSG and the LVSM are established and compared. It is revealed that the d-d channel impedance of LVSM behaves the negative resistor with a V-type magnitude in the low-frequency range, which easily interacts with the d-d channel impedance of the VSG and leads to instability of the system. Thus, the inductor current feedforward control and the additional voltage feedback control are proposed for the VSG to reshape its impedance. It diminishes the impedance magnitude and generates the active impedance of the VSG. In this way, the low-frequency interaction between the VSG and the LVSM can be mitigated. Besides, the proposed control preserves the dynamic performance of the system. Finally, simulations and experiments verify the effectiveness of stability analyses and the proposed suppression method.

Automated summary

This article investigates the instability problem caused by the interaction dynamics between the source-side virtual synchronous machine (VSG) and the load-side virtual synchronous machine (LVSM) in microgrids. The proposed inductor current feedforward control and additional voltage feedback control reshape the impedance of VSG, mitigating the low-frequency interaction between VSG and LVSM.