Design of power system stabilizer using robust control techniques

The power system is a dynamic system and it is constantly being subjected to disturbances. It is important that these disturbances do not drive the system to unstable conditions. Due to certain disturbances, electromechanical oscillations of small frequency set up. The kind of stability involved due to oscillations falls under small signal stability. The PSS has been found effective in damping such oscillations and ensure small signal stability of the power system. In this paper, the robust PSS have been designed to damp the rotor speed and rotor angle deviations with respect to time for SMIB power system. The PSS have been designed using H_∞ based robust control techniques. Here, the main focus has been to minimize the H_∞ norm of the linear fractional transfer function (LFT) which the transfer function matrix between the desired vector of commanded outputs to the vector of exogenous signals. The structure specified PSS in the form of PID has also been taken in the design based on H_∞ norm minimization using GA and PSO. The linear matrix inequality (LMI) technique has also been used to solve the H_∞ control problem to get PSS. Investigations have shown that PSS design using PSO and GA are superior to classical lead-lag and PID structures, and also to PSS designed using LMI technique.