IEEE PSS2B versus PSS4B: the limits of performance of modern power system stabilizers

IEEE Std 421.5 as revised by the IEEE excitation system subcommittee will introduce a new type of power system stabilizer model, the multiband power system stabilizers (PSSs). Although it requires two inputs, like the widely used IEEE PSS2B, an integral of accelerating power PSS introduced at the beginning of the nineties as the first practical implementation of a digital PSS, the underlying principle of the new IEEE PSS4B makes it sharply different. The present paper aims at assessing the two families of PSS´s from the point of view of their relative performance in tackling a wide range of system problems, using a single set of so-called robust/universal settings. Conclusions are drawn from a large number of small- and large-signal analyzes performed on several test systems and on an actual Hydro-Que´bec system, paying due account to the load models and governor response. Since either of the candidate PSSs can easily be tuned to perform acceptably in a standard local and/or inter-area oscillation scenario, emphasis will be put on comparing them at the inherent limits of the PSS concept, i.e., considering excessive VAR modulation during large generation rejection, fast load pickup on hydro units, and excessive torsional interactions during faults on large turbine-generators.