Evaluation of damping of subsynchronous interaction between direct-drive wind farm and LCC-HVDC based on the damping path analysis

The interaction between direct-drive wind farm (DDWF) and LCC-HVDC may make the power system more prone to subsynchronous oscillation (SSO). This paper presents a damping path analysis method to analyze and evaluate the subsynchronous interaction between them from the perspective of the internal disturbance transfer of the system. First, damping torque analysis (DTA) is extended to the SSO mode dominated by phase-locked loop (PLL), and the stability of the DDWF with the LCC-HVDC (DDWFL) system is analyzed. Then based on the closed -loop transfer function block diagram of the DDWFL system, the disturbance transfer process between DDWF and LCC-HVDC is revealed to analyze the interaction mechanism in the SSO mode, and the closed-loop disturbance transfer paths that reflect the system damping are called the damping paths. Further, damping path of the subsynchronous interaction between DDWF and LCC-HVDC is separated, and its effect on the SSO mode damping is evaluated by damping coefficient. It is concluded that the SSO mode dominated by PLL has instability risk in the DDWFL system, and the subsynchronous interaction between DDWF and LCC-HVDC provides negative damping to the system. Finally, the time domain simulation results demonstrate the validation of damping evaluation based on damping path analysis.