Mechanism Analysis and Enhancement Methods for Instability of LCC-HVDC System Caused by Series Compensation and STATCOMs

The mechanisms of LCC-HVDC system instability stimulated by series compensation (SC) and multiple STATCOMs are analyzed in this paper. The movement of dominant poles (MDPs) reveal that the SC will add a pair of mid-frequency poles to the system and deteriorate the system stability. For STATCOMs, increasing their online numbers will move the system poles at mid-frequency to left half plan (LHP) but move that at high frequency to the right half plan (RHP). Then, two approaches that can respectively improve the mid-frequency and high-frequency characteristic of the LCC-HVDC system are discussed, the effectiveness of which is verified by the simulation results of PSCAD/EMTDC.