When direct-drive wind farms are transmitted via flexible DC systems

the interaction between different wind farms

flexible DC converters and multiple equipment often results in sub-synchronous oscillations. Concerning this problem

this paper considers the interaction between the direct-drive wind farm and flexible DC converter station and builds the dynamic energy model of the interconnected system. According to the source of energy

the dynamic energy in the system is decomposed into four parts: the PMSG (permanent magnet synchronous generator) induction energy

the inter-generator interaction energy

the flexible DC induction energy and the generator-grid interaction energy. These four components characterize the respective contributions of the wind farm's inherent damping

the flexible DC system's inherent damping

inter-generator interaction

and generator-grid interaction to the system's overall stability. Then

based on the dynamic energy model of the system

the effects of PMSG integration distance

PMSG operation status

and flexible DC operation status on the stability level of the system are analyzed quantitatively. Finally

a model of a direct-drive wind farm transmitted via a flexible DC system is built in MATLAB/SIMULINK for simulation tests. The results verify that the interaction energy between the flexible DC converter station and PMSG and the interaction energy between the PMSGs with forced oscillation are the key factors that induce the oscillation.