Key Factors Analysis of Negative Electrical Damping for Sub-Synchronous Oscillation in Thermal Power units Induced by Flexible-HVDC

The negative electrical damping is the direct reason for the sub-synchronous oscillation in the near area where a large number of power electronic devices are connected to the power system. It is very important to understand the mechanism of electrical negative damping and to formulate suppression measures that determine the key links and parameters that cause electrical negative damping. To address this problem, firstly, the complex torque coefficient transfer function was expanded; the extreme value of electrical damping was defined; the key oscillation modes and fractions causing negative damping were determined based on mode decoupling by the electrical damping analysis method with improved complex torque coefficients. Secondly, the electrical damping correlation factor and sensitivity were introduced to determine the key influencing links and parameters of electrical negative damping, and the parameter adjustment scheme was given to suppress sub-synchronous oscillation according to the sensitivity analysis results. Finally, the time domain simulation of this method is verified by the PSCAD model..