Assessing Strength of Multi-Infeed LCC-HVDC Systems Using Generalized Short-Circuit Ratio

In this paper, a generalized short-circuit ratio (gSCR) is proposed for assessing the grid strength of multi-infeed LCCHVDC (MIDC) systems by the theoretical analysis of the relationship between static voltage stability and grid strength. The gSCR can resolve the ambiguity when applying the concept of shortcircuit ratio (SCR) for single-infeed LCC-HVDC (SIDC) systems to MIDC systems. Moreover, the gSCR is the generalized presentation of SCR in MIDC systems. Based on the gSCR, our defined critical gSCR (CgSCR) and boundary gSCR (BgSCR) for MIDC systems have the same functions as the critical SCR (CSCR) and boundary SCR (BSCR) used in grid strength analysis for SIDC systems. Also, the CgSCR and BgSCR have the same values as those of CSCR and BSCR (i.e., CgSCR = CSCR ≈ 2 and BgSCR = BSCR ≈ 3) to characterize the stability boundaries of MIDC systems. This allows the analysis experience of using the SCR, CSCR, and BSCR for SIDC systems can be easily transplanted to the application of the gSCR, CgSCR, and BgSCR for MIDC systems. The efficacy of the proposed gSCR along with CgSCR and BgSCR is demonstrated by comparing them with other indices of grid strength assessment for MIDC systems.