The configuration of hybrid receiving-end power grids fed by both line commutated converter based high voltage direct current (LCC-HVDC) and voltage source converter based HVDC (VSC-HVDC) systems is emerging

and accurately quantifying the stability margin of hybrid multi-infeed systems is crucial. The short-circuit ratio is often used to describe voltage stability margins in traditional LCC-HVDC multi-infeed systems. However

in hybrid multi-infeed systems

the mechanism and definition of the short circuit ratio (SCR) remain unclear. To address this issue

this paper proposes a method for quantifying the stability margin of hybrid multi-infeed systems based on the generalized SCR (gSCR) from the perspective of small-signal stability. Firstly

a small-signal admittance model for LCC-HVDC is established

and the impact of the phase-locked loop on the small-signal stability of LCC-HVDC is investigated using the synchronous dominant loop method. Secondly

the maximum singular value of the impedance matrix of VSC-HVDC is utilized in characterizing the voltage support capability of VSC-HVDC in hybrid multi-infeed systems. Finally

the gSCR is extended to hybrid multi-infeed systems

and a quantitative assessment method for the small-signal stability margin of hybrid multi-infeed systems is proposed. Simulation examples verify the effectiveness of the proposed method.