This paper presents a model-matching robustness design procedure based
on H-infinity-optimization theory for the robust redesign of nominal
controllers. The approach directly uses a control law designed for the
nominal operating condition and tunes the nominal control law to enha
nce the robustness with respect to the off-nominal operating condition
s. The procedure is applied to the design of a power system stabilizer
(PSS) for a single-machine infinite-bus system which has a range of p
ossible operating conditions. The results show that the redesigned con
troller contains features similar to the nominal controller, but yet i
mproves significantly the damping of the machine swing modes at the of
f-nominal conditions.