Impedance Circuit Model and Instability Mechanisam Analysis of Grid-Forming MMCs with Virtual Admittance Control

Le résumé fourni par la source

Modular multilevel converters with grid-forming control (GFM-MMCs) are increasingly recognized as a significant solution for improving power system oscillatory stability, especially in weak grid scenarios. Virtual admittance control (VAC) has been employed for current limiting in GFM-MMCs. However, a common challenge is balancing the fault current suppression capabilities of VAC with its oscillatory stability performance. In this paper, the control links of the VAC-based GFM-MMC are first represented as virtual resistors, inductors, and capacitors. This circuit-theoretic perspective offers insights into the negative resistance characteristic affected by the interaction between VAC and the current inner loop control. Then, the mechanism of oscillatory instability for GFM-MMC with VAC has been investigated using the established circuit model. Finally, the instability analysis is confirmed through simulations conducted using Matlab/Simulink.

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