The paper presents an adaptive fuzzy logic power system stabilizer (PS
S) design for damping oscillatory electromechanical modes of oscillati
ons and enhancing the first-swing synchronous stability margins. The n
ovel design utilizes a multivariable damping signal vector consisting
of machine speed deviation, rate of speed deviation, and voltage devia
tion. The design is based on a multizonal PID structure and fuzzy logi
c variable-gain scheduling to optimize the damping action. The fuzzy l
ogic PSS is proposed for use in parallel with the conventional analog
type PSS with added simple switching criteria. The two PSS blocks can
be allowed independent, sequential, and/or combined operation with dif
ferent effective stabilizing weighting. The paper investigates an indi
vidual conventional PSS, a rule based fuzzy PSS, and hybrid operation.
The parallel operation of a conventional PSS and a fuzzy logic one pr
ovides optimal sharing of the camping action under small- as well as l
arge-scale generation-load mismatch or variations in external network
topology due to fault or switching conditions.