A free-model based controller design and its application to power system stabilization

This paper presents the free model approach for a closed-loop system identification using input and output data and its application to design a power system stabilizer (PSS). The free model concept is introduced as an alternative intelligent system technique to design a controller for an unknown dynamic system with input and output data only, and it does not require the knowledge of mathematical model for the system. In the free model, the data used has incremental forms using backward difference operators. A linear transformation is introduced to convert the free model into a linear model so that the linear quadratic regulator (LQR) design method can be applied. The feasibility of the proposed method is demonstrated in a three-machine nine-bus power system. The LQR method is applied to the free model to design a PSS for the system, and compared with the conventional PSS and LQR controller based on the ARMA-model. The free-model based PSS is robust in different loading conditions and system failures.