Some reference papers discussed how the performance of a
feedback system can be described in terms of the location of the
roots of the characteristic equation in the s-plane [1-8]. It is
frequently necessary to adjust one or more system parameters in
order to obtain suitable root locations.
The root locus method was introduced by Evans in 1948 and
has been developed and utilized extensively in control
engineering practice [1-3]. In fact, the root locus method provides
the engineer with a measure of the sensitivity of the roots of the
system to a variation in the parameter being considered. The
root locus technique may be used to great advantage in
conjunction with the Routh-Hurwitz criterion.
The root locus method provides graphical information, and
therefore an approximate sketch can be used to obtain
qualitative information concerning the stability and
performance of the system. Furthermore, the locus of roots of
the characteristic equation of a multiloop system may be
investigated as readily as for a single-loop system. If the root
locations are not satisfactory, the necessary parameter
adjustments often can be readily ascertained from the root locus
[4].