Power system stabilizer design using out of phase torque correction method

The need for power system stabilizers (PSS) in interconnected power systems has become essential to damp low frequency oscillations and enhance the system stability. Conventional PSS design techniques utilize local measurements, hence allowing the use of single machine infinite bus method to tune the PSS parameters. However, these techniques do not provide a direct method to calculate the PSS gain. In this work, an explicit expression based on frequency analysis was derived that relates the PSS function and generator electrical torques. It showed that the torques developed at poorly damped modes have large imaginary component that do not contribute to damping. The PSS is tuned to correct the phase of these torques, thus, provide positive damping. The proposed method was examined on several test systems namely two-area four-machine, IEEE9, and IEEE39-bus system. Besides successfully improving the system damping, the proposed method was found to be robust at different loading conditions