Small-Signal Stability Assessment of Multi-Inverter Medium-Voltage Grids Using Impedance-Based Methods

Abstract:
The transition of energy supply from fossil fuels to renewable energies is changing the power system in unprecedented ways. One aspect of this transition is the replacement of synchronous machine-based power generation with powerelectronic inverters. The fundamentally different dynamics of inverters compared to synchronous machines raise stability concerns in inverter-based power systems. This work aims to contribute to the research on inverter-driven stability issues, focusing on the medium-voltage (MV) level. Using impedancebased stability analysis, the impact of several control parameters of grid-following (GFL) and grid-forming (GFM) inverters on the small-signal stability of a MV multi-inverter test grid is studied. Several causes for stability issues are identified, including PLL bandwidth, GFM droop control and grid-support control. Additionally, the accuracy of the impedance-based stability analysis is investigated by validating the results with time-domain simulations, revealing accuracy issues for certain study cases.