Low frequency oscillations can cause power system instability. This paper introduces a proportional integral (PI) controller according to Fuzzy-Sugeno logic (FPI) for a thyristor controlled series capacitor (TCSC) in order to improve the stability and to damp the low frequency oscillations. This controller is used with a lead-lag controller for a power system stabilizer (PSS) in a single-machine infinite-bus system. Also, an independent fuzzy controller for PSS is designed to demonstrate the capability of FPI controller. Three following compositions of the controllers are implemented to control TCSC and PSS at the same time: (I) two lead-lag controllers together for TCSC and PSS, (II) a fuzzy controller for PSS with a lead-lag controller for TCSC and (III) a lead-lag controller for PSS with a FPI controller for TCSC. Simulation results show that the designed fuzzy and PI (FPI) controller is robust against different loads and faults.

Keywords: Thyristorcontrolled series capacitor (TCSC), Power system stabilizer (PSS), Fuzzy logic, Proportional integral (PI) controller, Takagi-Sugeno