Design of H∞-PSS using numerator-denominator uncertainty representation

This paper presents a new method of designing a robust H_∞-PSS to deal with some limitations of the existing H _∞-PSSs (standard H_∞-PSSs). These limitations include: (i) the inability to treat the system uncertainty when a stable nominal plant becomes an unstable perturbed plant; and (ii) the cancellation of the plant´s poorly damped poles by the controller´s zeros. The proposed multiple inputs single output controller for the excitation system is based on the “numerator-denominator” uncertainty representation which is not restricted in the modeling of uncertainty as compared to the standard additive or multiplicative uncertainty representation. Furthermore, the bilinear transformation has been used in the design to prevent the pole-zero cancellation of the poorly damped poles and to improve the control system performance. Simulation results have shown satisfactory performance of the proposed PSS for a wide range of operating conditions and good stability margin as compared to both the conventional PSS and the standard H_∞-PSS