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This letter proposes an adaptive hybrid grid-following (GFL) and grid-forming (GFM) control, which ensures small-signal stability of inverter-based resources (IBRs) with ultra-weak and very strong grid connections. The hybrid control offers mixed GFL and GFM characteristics by altering the grid synchronization and outer loop controls. The proportion of GFL or GFM features is adaptively adjusted by using the analogy of a hysteresis loop in response to the short-circuit ratio (SCR). Consequently, the GFL characteristics are gradually reinforced as the SCR increases. Impedance-based analysis and electromagnetic transient simulation results confirm that the proposed control enhances the system's small-signal stability from ultra-weak (SCR=1) to stiff (SCR=50) grids.
Liu et al. (Tue,) studied this question.