Abstract
The small-signal stability of the line commutated converter based high voltage direct current (LCC-HVDC) system connected to weak AC grid is of great interest. However, relevant studies lack quantitative analysis of stability margin and interaction between different control loops. This paper completely derives the single-input single-out (SISO) feedback control model of LCC inverter station. On this basis, the influence mechanism of AC system strength on system stability is investigated according to the Bode diagram, and corresponding margin indexes are given. Meanwhile, the interaction between different control loops is analyzed. Results manifest that as the AC system strength becomes weaker, the system stability margin is diminished, and the coupling intensity between DC voltage controller (DVC) and phase locked loop (PLL) increases.
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