The photovoltaic (PV) power station connected to the voltage source converter-based high voltage direct current (VSC-HVDC) system not only transmits power but also introduces the risk of oscillations. The existing small-signal stability (SSS) analysis methods typically simplify computational complexity by neglecting the dynamic differences between individual PV units in PV power stations. However

in practical systems

there are differences in active power output or control parameters of PV units

which may lead to errors in small-signal stability analysis results. Therefore

the impact of differences in active power output or phase-locked loop (PLL) control parameters of PV units

which are PLL-dominated

on SSS of the system is analyzed in the sub-synchronous frequency range. The results show that the differences in active power output or PLL control parameters of PV units may affect the position of dominant oscillation mode in complex plane

while the stability boundary is determined solely by the minimum and maximum values of corresponding parameters of all PV units. Therefore

an interval estimation method is proposed to predict the range of dominant oscillation modes of PV units under different active power outputs or control parameters

which enables rapid SSS assessment while considering the dynamic differences of PV units

and provides a reference for oscillation warning in practical systems. Finally

the effectiveness of the proposed method is validated through simulation examples.