直驱风电场经LCC-HVDC外送系统阻抗建模及振荡机理分析

The energy sources and main consumption are unevenly distributed in China, causing the pressing need for large-scale long-distance transmission of wind power. The direct-drive permanent magnet synchronous generator (D-PMSG) based wind farm integration through line-commuted converter high voltage direct current (LCC-HVDC) system has become a common way to deliver the wind power. However, the interaction between the wind turbines connected to grid through the power electronics devices and LCC-HVDC has not been thoroughly investigated, and the potential oscillations may seriously affect the safe operation of the power grid. In this paper, the frequency-domain expression of AC/DC mapping function was obtained by using double Fourier transform, and the impedance model of the D-PMSG-based wind farms integrated through LCC-HVDC system was established. Based on the analysis of the dominant factors in each frequency range, the impedance characteristics were discussed, and the factors that have significant influence on the impedance characteristics in sub-synchronous and super-synchronous frequency band were studied in depth. Finally, the oscillation risks of the system in sub-synchronous and super-synchronous frequency bands were revealed and verified by time-domain simulation, and the oscillation mechanism was presented.