Comparative Analysis of Damping Mechanisms in Grid‐Forming Inverters Under Single‐Loop Voltage‐Magnitude and Dual‐Loop Vector Voltage Controls

ABSTRACT With the widespread adoption of grid‐forming inverters (GFMIs), the integration of renewable energy into the grid may induce sub‐synchronous oscillations (SSO). Existing studies have focused primarily on the power‐loop behavior in instability mechanisms, while systematic comparisons of the distinct instability cause arising from the two widely used inner loop controls—Single‐Loop Voltage‐Magnitude Control (SLVM) and Dual‐loop Vector Voltage Control (DVVC)—remain scarce. In this paper, a unified positive‐sequence impedance framework is established for SLVM and DVVC under consistent assumptions and within the same sub‐synchronous band, linking controller parameters to impedance‐based stability characteristics, thereby enabling a like‐for‐like attribution of negative‐damping mechanisms. Results indicate that both SLVM and DVVC controls exhibit distinct negative damping dominant factors in the sub‐synchronous frequency range. Compared with DVVC control, SLVM control produces significantly weaker negative damping effects, thereby enhancing GFMI's stability in stronger grid‐connection scenarios. Impedance analysis and experimental tests validate these findings under different grid conditions.