The application scenarios of direct-drive wind farms (DDWF) coupled to line-commutated-converter-based high voltage direct current (LCC-HVDC) AC buses have increased. The problem of forced subsynchronous oscillation (FSSO) caused by the inherent mode of the system being excited by subsynchronous interharmonics generated by LCC-HVDC modulation is becoming increasingly prominent. To address this issue

this paper first derives the time-domain expression of FSSO during the interharmonics disturbance generated by LCC-HVDC modulation. Then

the mechanism of subsynchronous interharmonics excitation coupled with wind farm FSSO for this system is proposed. Based on the FSSO mechanism

a parameter optimization strategy is proposed to mitigate the FSSO: first

to enhance the damping of the excited subsynchronous modes; second

to keep the oscillation frequency of the excited subsynchronous modes as far away as possible from the frequency range of the interharmonics; and third

to take into account the dynamic characteristics of the fault ride through. Then

the wind power system control parameters associated with the modal damping characteristics and oscillation frequencies of the coupled system are identified. A wind farm parameter optimization strategy for mitigating FSSO that integrates modal damping

the degree of deviation of modal oscillation frequency from the interharmonics frequency

and the fault ride-through performance of the wind farm is proposed. Finally

the system model is built using PSCAD/EMTDC time-domain simulation to verify the correctness of the theoretical analysis and the effectiveness of the optimization strategy for mitigating FSSO parameters.