Series compensation of transmission lines using fixed series capacitors can cause sub-synchronous resonance (SSR) between electrical and mechanical systems. This phenomenon leads to severe damages to turbine generator shafts. Thyristor controlled series compensator (TCSC) is one of the FACTS devices which can be utilized to damp electromechanical and sub-synchronous oscillations. This device can perform flexible series compensation and SSR damping. The effect of different parameters of the TCSC is studied using complex torque coefficient method. Open loop and closed-loop constant current and constant power control methods are simulated using PSCAD/EMTDC software package. First IEEE benchmark model for sub-synchronous resonance studies and a complete model of TCSC is used to analyze the effect of different parameters and control structure on the SSR damping capability of the TCSC.

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