An approach to PSS design for transient stability improvement through supplementary damping of the common low-frequency

The authors propose an uncommon structure for the power system stabilizer (PSS) transfer function to improve the damping of the system low-frequency (in the range of 0.02-0.08 Hz), as well as the usual local and inter-area frequencies (in the range of 0.2-2.5 Hz). These somewhat conflicting goals are achieved by adding the speed-based stabilizing signals of two compensation filters, which independently provide the phase of adjustment necessary for adequate damping torques at two widely separated center frequencies (i.e., 0.05 and 1 Hz). Modeling of the open-loop system via the Prony analysis of the multimachine pulse response, followed by a root-locus study, made it possible to determine analytically the supplementary damping provided by the new PSS in the two frequency ranges of interest. Simulations of large disturbances on a realistic Hydro-Quebec transmission network with more than 59 machines modeled in detail confirmed that on a fast responding hydro-plant with significant installed capacity, the new PSS can add considerable damping to the 3c/min system oscillation, without any direct supplementary control of the governor